Hi,
You can apply to the Registrars' Office direct, depending if you know which area the event took place. For Glamorgan, in Wales, for example, they charge £8.00 per (not sure what that converts to) certificate and they are handwritten copies (not typed). The maximum time for delivery is around fourteen days (oversea's would, obviously, take longer). Details of all Registrars' Offices addressess can be found on the web. You don't need a 'middle man' to obtain such documents.
Regards
Anne