Sorry to be the bearing of bad tidings but you cannot work in the UK for hire or reward unless you have a Class 1 medical. This includes banner towing, instruction, cargo haul etc.
Class 2 (for pleasure flying - ie. PPL) is a little more lax - check out
www.srg.caa.co.uk/pld/med/med_information.asp?page=/medical/SRG_MED_jaa_class_2_vision.htm for the low-down on the CAA/JAA class 2 medical (visual) requirements for a PPL. According to this site, the maximum corrective error is -8.00 dioptres including astigmatism, but you could still try getting the Class 2. I would suggest you follow the CAA's advice (for once!) and get a copy of your current eyesight prescription and then call an approved medical examiner to discuss your circumstances before forking out £125 or so for your Class 2. Good luck, but I'm afraid a flying career in the UK is out...
Can't speak for foreign authorities - you may get details off their websites perhaps...