You can book a theory or driving test from here, or just get some help with your driving.
http://www.direct.gov.uk/booktheorytest
http://www.direct.gov.uk/changetheorytest
http://www.direct.gov.uk/bookpracticaltest
http://www.direct.gov.uk/changepracticaltest
http://www.2pass.co.uk/ Really useful website for learner drivers
http://www.smartdriving.co.uk/ Similar to above