
If you're keeping the same photocard you just have to phone them with your credit/debit card details and they'll post one out really quickly to you.
from the directgov website...
You can apply by phone if one or both parts of your photocard licence have been lost or stolen and none of your details have changed. DVLA accepts the following credit or debit cards - MasterCard, Visa, Eurocard or Maestro and the fee is £20.00. The telephone number is 0300 790 6801, Monday to Friday 8.00 am - 8.30 pm or Saturday 8.00 am - 5.30 pm.