Sofia is right, architect's training and education takes 7 years so clients do get a little extra by engaging an architect although I couldn't imagine anyone taking 1,000 hours to design a loft conversion!
Sorry but I am nowhere near the south east so can't help directly but a a guide as to what I as an architect would usually charge - around £1,500 to £2,000 for an 'average' loft conversion prvided there were not too many structural complications or protracted negotiations with the local authority. Added to this the client would have to pay the application fees for Building Regulations apprval (and planning consent if required) direct to the LA.
For such a fee, a client would get an hour's free initial consultation, measured survey, production of sketch proposals followed by drawings and calculations sufficient for the application. In addition I would include purchase of the ordnance survey CAD file, a design and access statement (if required), fill in the forms - sometimes these can be very confusing for clients - and allow a little time to help with Party Wall notices.
Finally, I would deal with any queries from the LA free of charge.
As I said, if there were complex structural or other specialist matters then I would ask the client to engage an engineer or specialist to assist.
If the client wanted additinal services e.g. detailed construction drawings and a specification, then I would agree a further fee.
Hope this helps.
(BTW I can only dream of £250 an hour! :)