Feedback - There is, in effect, the £10 surcharge if you buy at a Travel Shop. The fare displayed by the computer is automatically £10 more than the fare quoted on ba.com (or on other Internet sites) so unless you were aware of the fare that would be charged by ba.com you would never be aware that you were paying £10 more.
In the end, I saved the vouchers to buy a single ticket, so there was some overall value left in the exercise for me. Well, maybe not when taking into account the time spent getting there and back but I was assisted by a friendly and very efficient agent so it was a good break from work.