Hi & Welcome --- Perhaps you may take off your CAPITAL lock when posting, it's considered shouting and is bad forum etiquette... Thanks.
You could consider the cheapest third party (is that what you meant by RTA= road traffic accident ? ) temporary cover on the old car, in order to transport your number plate across, you can get temporary cover for the short period you need it from here if you like > http://tempcover.com/default.aspx?src=google for long enough to transfer the number once you've got the temp cover note then, you need to do the following below :
When you wish to transfer your registration mark, you will need to fill out a V317 form and either take or send your application to your local vehicle office along with the following documents (for each vehicle):
• V5C Registration documents (or completed new keeper’s supplements with V62 form)
• MOT certificate(s) (if applicable, i.e. more than 3 years since first registration)
• Photo copies of Valid tax discs (or V10 form(s) along with certificate(s) of motor insurance and appropriate payment for new tax disc(s).
• Cheque for £80 made payable to the department of transport.
The Donor vehicle (the one that the registration is coming off) will receive an age related registration mark.