The decision has been called "a stitch-up"
Mayor of London Boris Johnson finds himself leading the campaign for the UK to leave the EU tonight.
It's after his Vote Leave group was named as the main voice calling for a Brexit in the upcoming referendum.
The decision's been called a 'stitch-up' by part of an opposition group - which says it's considering legal action.
Claire Bassett is from the UK Electoral Commission:
Last month, Johnson claimed that the Brexit could help tackle terrorism problem:
"We are thinking today particularly about how to combat terrorism and the threat that that poses to our societies. I've seen various people quoted as saying that remaining in the EU is essential for security.
"I think it's important to put a countervailing point which is that there are some ways now that the European Court of Justice is militating against our ability to control our borders in the way we want to and indeed to maintain proper surveillance".