This is what EF comes up with (assuming you are are a UK national & resident), which I am fairly sure comes from Timatic and will be what the airline agent will see when doing the visa/document check:
Code:
Information as of 01AUG16 / 1428 UTC
National United Kingdom (GB)
Embarkation United Kingdom (GB)/Transit India (IN)
Destination Sri Lanka (LK)
ALSO CHECK DESTINATION INFORMATION BELOW
India (IN)
Visa required, except for Passengers with an Overseas Citizen
of India" card or booklet, or:
Visa required, except for Passengers with a "Person of Indian
Origin" card, or:
TWOV (Transit Without Visa):
Visa required, except for Holders of confirmed onward tickets
time of 24 hours.
- Hotel facilities are available in Terminal 3 at Delhi (DEL),
provided holding boarding card for connecting flight.
Additional Information:
- Holders of visas that specifically state the city/airport of
entry must enter India at the specified city/airport.
India (IN)
Passengers arriving within 6 days after leaving or transiting
and not holding a yellow fever vaccination certificate will be
quarantined for 6 days. Quarantine facilities are only
available at Delhi (DEL), Chennai (MAA) and Mumbai (BOM). At
other airports passengers will be deported.
If holding a yellow fever vaccination certificate prior to
arrival, the certificate becomes valid 10 days after
vaccination and will stay valid for life.
Exempt from Yellow Fever vaccination:
- Children under 6 months of age.
- Passengers transiting India by the same aircraft.
- Passengers transiting countries with risk of yellow fever
transmission provided not leaving the transit areas.
Sri Lanka (LK)
Passport required.
- Passports and other documents accepted for entry must be
valid for a minimum of 6 months from the arrival date.
Passport Exemptions:
- Passengers with an emergency passport.
- Passengers with a temporary passport.
Visa Issuance:
Visa required, except for Holders of passports issued by
United Kingdom can obtain a visa on arrival for a max. stay of
30 days. Fees vary and must be paid in USD. Extension of stay
possible for additional 150 days. (SEE NOTE 51704) (SEE NOTE
56148)
NOTE 51704: Passengers traveling as tourists must obtain
.
NOTE 56148: Passengers traveling for business must obtain
an ETA before travel from a Sri Lankan representation
abroad.
Visa required, except for Passengers with an emergency
passport can obtain a visa on arrival for a maximum stay of 30
days if holding a return/onward ticket and an ETA obtained
prior to arrival. Fees vary and must be paid in USD.
Visa required, except for Passengers with a temporary passport
can obtain a visa on arrival for a maximum stay of 30 days if
holding a return/onward ticket and an ETA obtained prior to
arrival. Fees vary and must be paid in USD.
Additional Information:
- Visitors must hold proof of sufficient funds to cover their
stay and documents required for their next destination.
Warning:
- Nationals of United Kingdom not holding return/onward
tickets could be refused entry.
Sri Lanka (LK)
Passengers arriving within 6 days after leaving or transiting
, Sao Tome and Principe, Somalia or Tanzania and not holding a
yellow fever vaccination certificate are subject to quarantine
for 10 days.
If holding a yellow fever vaccination certificate prior to
arrival, the certificate becomes valid 10 days after
vaccination and will stay valid for life.
Recommended:
- Malaria prophylaxis: malaria risk, mainly due to P. vivax is
low and exists throughout the year, except in the districts
of Colombo, Galle, Gampaha, Kalutara, Matara and Nuwara
Eliya. Recommended prevention in risk areas: A.
- VIET NAM: TEMPORARY VISA EXEMPTIONS
EXTENDED