Are Keeping In Touch days paid at normal salary rate?

[oysterpots]

Boss has suggested I might like to come in next month but frankly if I'm not getting paid I'm not going to bother!

I don't think they have to be, is up to you to negotiate. I work for the nhs, and assume they will be paid at normal salary rate.
I am considering using mine in the next few months and wondering how I 'register' them so i get paid, do i call up payroll and tell them??

You need to negotiate, so if you are coming in for a normal day's work, you should obviously negotiate a normal day's pay, but sometimes these things might be used for a meeting or something taking a couple of hours, which is why it's not set in stone must be a normal day's pay.