Ah which would I prefer. Brussels, at the moment is more money, I know the people and it's a real PITA to work in. I don't like Brussels as a city to live in, it's expensive and the government is becoming really aggressive with foreign workers and all sorts of registration.
London is an unknown but the people seemed reasonable, they know they're not super good at what they are doing and they're trying to improve and want help. The money is less but, interestingly, I can get accommodation more easily and cheaper than in Brussels. Travel is a bit more problematical but could, with a fair wind, be cheaper and faster.
However here's the consideration. With the whole mess of Brexit, who knows what is going to happen. My own personal feeling is that the £ is going to jump in value and that working relationships are going to fray due to the tensions. So I could wind up in a job which is paying less money, giving me more hassle to work at and with the expectation that I'll stay for years.
In the end, six months in London looks like risk mitigation to me and, as a PM, I'm all about risk management...
There is still, also, the risk factor of Brussels being a higher priority terror target than London, right now.