The Answer;
In the name of Allah, Most Gracious, Most Merciful.
A Nikah does not amount to a Civil Marriage in the UK. A Nikah as conducted by an Imam, is not considered a Civil Marriage without an official Registry. London Fatwa Council recommends all wedding parties to have their marriage officiated at the time of Nikah. Find further information on this process here.
And Allah(swt) alone knows best.