Last week of February, but as you're in the North East, probably early to mid March, depending on weather conditions at the time. You have a shorter growing season than the South where you are, so if you leave it too much later to hard prune, the plants may not put on enough growth to produce much flower this year.

After the harsh frosts. We are 4 miles from the sea in the south West and I leave mine until March - remember that minus ten we had in March a couple of years ago?.

I've never had any losses doing mine and my customer's roses in mid February as long as a hard frost isn't expected for a day or two.(mid latitude UK)

I'd concur with Anchorman's comment - I've done 'em with snow on the ground last week of February, melting snow, admittedly, but they were fine.

Thank you for all your help.
My neighbour is going to NZ in a fortnight until the end of May and she is taking my advice to prune before she ships out.