Just thought I would share the email from the UK Embassy.
Apologies if it has already been shared.
Interestingly they advise against VOA and are very expensive

If you are enquiring about visa, please find all the relevant information below. Your other requests will be responded in due course.

BUSINESS VISA

Starting from 1st Jan 2015, the Embassy of Viet Nam temporarily stop processing Business visa application without Approval Letter due to the introduction of new Immigration Regulation. If you travel to Viet Nam for business purpose, your host organizations/partners/invitees in Vietnam will need to arrange your visa Approval Letter directly with the immigration office. The Embassy will issue business visa when the Approval Letter is submitted along with the application form and passport.
The Embassy may consider specific requests for business visa. Please contact us at [email protected].

TOURIST VISA

- Visa fees and bank account are listed at the end of this message.
- The quickest way to apply for visa is by email (you have to bring
your passport to the embassy to collect the visa). WE DO NOT ISSUE
VISA ON THE SAME DAY (see Processing time below)
- If the online form does not work, please print out the PFD form and
complete by hand (download form here:
http://vietnamembassy.org.uk/visaformf.pdf)
- The embassy only issues 30 days and 90 days visa.
- For non-EU passport holders (excluding Australian, USA, Canadian),
the visa process may take longer, please contact us for more
information.

- Upon receipt of your visa, you are required to make sure all
information on the visa is correct (especially passport number and
visa date). Any error must be notified to our staff immediately and
BEFORE your departure from the UK and Ireland. Failure to do so means
we will NOT take any responsibility when visa problems arise upon
arriving in Viet Nam and no refund and compensation will be available.

Travelers need to obtain standard visas from the Embassy of Vietnam before going to Viet Nam. We do not recommend visa-on-arrival and online visa (many offers on the internet for these type of visa are scams). Visa issued by the embassy of Vietnam is fully valid, you are
not required to pay any other fee upon arrival.

- To apply for a stick-on Visa from the embassy, please summit the
following documents: (1) an application form (to be completed online)
with a passport photo (standard UK Paspport photo) attached, (2) valid
passport. (Other documents may be requested when necessary). (3) Visa
fee payment (see full list of visa fee at the end section)

You can apply for Visa in person or by post. A third party can submit
relevant documents and collect visa on your behalf. Email application
is also possible if you use express visa service.

- Visa form has to be completed online here: http://visa.mofa.gov.vn/Homepage.aspx

The form has to be printed out if you apply in person or by post. If
you apply by email (see below) please save the PDF file and send as
attachment. (If the online form does not work, please print out the
PDF form and complete by hand, download form here: http://vietnamembassy.org.uk/visaformf.pdf
Please make sure all the information provided in the application form is correct. We will not
take any responsibility for the incorrect visa which is caused by the
errors in the application form.

- TYPES OF VISA: You do not need a visa to enter/re-enter Vietnam if
you do not cross immigration checkpoint when catching connecting
flights. SINGLE ENTRY visa is when you only entering Vietnam (crossing
border control) once. MULTIPLE ENTRY visa is when you enter Vietnam
(crossing border control) more than one time (re-entering Viet Nam
after leaving for another country). If you are traveling on a CRUISE,
please check with your tour organiser for the type of visa required.

- CHILDREN with their own passports have to apply for Visa.

- WHEN TO APPLY: You can apply for visa 6 months before traveling.

- Embassy address: 12 Victoria Road, London W8 5RD

- DATE OF ENTRY: The Visa will be valid from the Date of Entry
provided in the application form and extend for 30 or 90 days,
depending on Visa type. You can travel to Vietnam at any time after
(or on) the date of entry and must leave before the visa expires. If
you are unsure of your exact travel date, please put an early date to
allow yourself maximum flexibility.

- PROCESSING TIME: We do not issue visa on the same day. Regular
processing takes 5 working days. Using express service you can obtain
a visa the next day or 2 days later.

- APPLYING IN PERSON: Visa submission hours: 9:30-12:30 Monday to
Friday. No appointment needed. A third party can submit relevant
documents and collect visa on your behalf. PAYMENT: All fees must be
paid in CASH if you apply in person at the Embassy. The passport will
be kept at the embassy and can be collected after 5 working days with
the visa.

- APPLYING BY POST: please provide a self-addressed envelop (not
stamped) and Postage charge and Handling fee for returning your
passports: £8 for one passport; between 2-3 passports: £6/each
passport; between 4-7 passports: £5/each passport. Please note: if you
send a prepaid envelop, there is still handling fee of £3/passport.
All passports are posted by Royal Mail Registered post, express
delivery. PAYMENT: If application is made by post, please pay by
cheque or postal order payable to EMBASSY OF VIETNAM, (write your
name, telephone number, date of birth at the back), all in British
pounds only. Visa fee and postage charges can be paid by one
cheque/postal order/bank draft (when applying by post). DO NOT PAY BY
BANK TRANSFER IF YOU APPLY BY POST. Please post your application to:
Vietnam Embassy, 12 Victoria Road, London, W8 5RD.

- EMAIL APPLICATION (for express service only): Your application must
be submitted before 12.30 PM of each working day (email to:
[email protected]) and payment by bank transfer made
before 12:30PM. The complete application include: (1) Visa application
form (completed online, saved as PDF file and attached to the email);
(2) Copy of the photo page of your passport; (3) Confirmation of
payment of the visa fee. To collect the visa, please visit the embassy
with your passport. Someone else can collect the visa for you if
he/she brings your passport. Important notice: your email must say
“Visa application” in the SUBJECT section. Failure to do so may lead
to your mail being classified as junk. Your application is not
accepted unless you receive the confirmation email within 24 hours.
Once the confirmation email is sent, it is not possible to cancel your
application; payment of the full visa fee is required. Amendment of
the visa date will cost £30.

Embassy’s bank account name (FOR EMAIL APPLICATION ONLY): Embassy of Vietnam
Add of account owner: 12, Victoria Rd, London W8 5RD
Bank account: 25894293
Sort code: 50-30-10
IBAN: GB 86 NWBK 503010 25894293
Swift code: NWBK GB 2L
Bank name: Natwest
Address: Kensington Royal Garden Branch
55, Kensington High Street London W8 5ZG (THIS IS NOT THE EMBASSY’s
ADDRESS – Do not post your passport to this address).

Postage charge: £8 for one passport; £12 for two passports

VISA FEES (not including postage charges) are as follows:
(Please note visa fees are the same for all age groups and for all
nationalities.
When applying by post, all fees can be paid by ONE cheque or postal order).

Tourist Visa Fees (Per passport):

- 30 days, single entry: £54 (regular process takes 5 working days).
Express service: £69 (2 day service), £75 (next day service).
- 30 days, multiple entry: £85 (regular process takes 5 working days). Express service: £105 (2 day service), £115 (next day service)