In message . com,
DrTeeth writes

Wow - thanks very much all for the speedy (and detailed) replies. Will
have a bit of luggage with me so was thinking taxi but someone had
suggested that this could cost as much as £20 for a 5 mile journey
(seems a bit much)

It depends on the time taken as much as the mileage. On a Sunday evening
at 8pm Paddington to Old Street might be a bit less than £20 - but not a
lot!

--
Paul Terry