This may be counter to a lot of the comments here, but please, please, please don't hand in your notice until you have another job offer. I did this a few years

This may be counter to a lot of the comments here, but please, please, please don't hand in your notice until you have another job offer. I did this a few years ago, and ended up doing crappy temp jobs for months. My savings ran out, I lost all confidence in myself and became visibly nervous in interviews. This created a positive feedback loop as I became more and more desperate. It took me years to fully recover from the experience. I should add that I was not a developer at the time (I came to programming somewhat late), but I think this advice applies to any job. I never fully appreciated the suspicion you're treated with if you're not currently employed. I don't know if this is a cultural thing (I'm also in the UK). It raises a whole lot of extra questions that you really don't want to have to answer. I've read that some employers even use it as a filtering criterion. So by all means listen to the other responders and make a definite decision to leave, apply to every job you can. Book some annual leave to attend interviews. But please don't resign until you've accepted another job offer.