we use a brand called BFT they sell a assembly that fits onto the existing door that converts it to electric operated, then you just add on remote radio to operate...simple to fit
youre in newcastle too so why not give this place a call they are up in cramlington (bft dealers) we get all our electric garage stuff here. http://www.nortechgaragedoors.co.uk/contact.htm
this is the product i've fitted to garage doors to convert them into electric ones... http://www.gates.uk.com/products/garage-door-automation