V5 & tax is dealt with by the process of assigning the number. In addition to this you should ....

1) inform your insurance company in writing and obtain updated documents..

2) if you have finance on the car, inform the company that provides it in writing and obtain updated documents.

3) inform your dealer/manufacturer in writing with regard to service & warranty.

Other than that you can't assign a number/prefix which would make the car appear newer than it is... eg you can't put XY10 BOB on ??09 ??? or anything < 10 or with the older style you can't put T123 BOB on S??? ??? or anything older than T reg.

The two best known companies are new-reg & reg transfers. It worth a phone call to haggle despite the 'web price' and 'web only' blurb on the web sites.

Edited by AnotherWaiting on 26/11/2010 at 19:09

.Also what do i do about documents(log book,road tax etc)

Have a look at the DVLA site for the process:

tinyurl.com/y9bvaly