Thank you all for your comments. It's always so interesting to hear about other people experience and sometimes puts things into perspective.
I have made my decision and decided to take the job!!!!!

I will only tell my boss when I get back from my hol's next Thursday but I confirmed with the new company and I am already going to a medical tomorrow!!!!
I think the stress factor was pretty much decisive. I talked it through with my boyfriend last night and slept on it, so here we are! I called my 'new boss' this morning to confirm and he was delighted.
Thank you all
Bea