Take your concealed carry permit and 40 cal Glock 22.....ohhhhh, wait, you're in the UK. Scratch that idea. Take a concealed phone to call the coppers when it's too late for them to help.
But seriously, I would either back out altogether or take some muscle with you. Show up early, scope out the place and make a Go-No Go decision. Don't do the meeting indoors, unless it's a busy and respectable hotel lobby. Do it outside, in the daylight and in plain view of bystanders. Unless the bystanders are dirt bags in which case they wont care what happens to you anyway, and they might be in on it themselves.
The Golden Rule: If it makes the hair on the back of your neck stand up and gives you butterflies in your stomach and something just doesnt seem right, than it probably isn't right so jump ship!