Sammy is an excellent trainer. He's trained loads of people I know and also trains my son in football. He is based in Finsbury Park not the area but the park. Message me and I'll give you his number.
Viki is my PT and she trains in Priory Park (which helps keep the costs down) - http://zest-personaltraining.co.uk/
Bex Borrows at Bexercise is great. Otherwise BMF in Finsbury Park is fantastic for all levels of fitness. It's a really welcoming and fun environment and you'll definitely get fitter quickly and make a few new friends. It's pretty cheap too.
Yosdani +44 7960 839026
I’m training with him! I saw my body changing very quickly!
Pennie Varvarides at Puregym Finsbury Park