Welcome Declan. I may have misunderstood your post but are you saying you exposed paper to white light( no neg and from the enlarger presumably?) for up to 1.5 mins and it was still grey?

This seems an incredibly long exposure to be still producing grey. I have had a similar problem but never at such long exposure. Mine was the result of paper which had exceeded its useful life.

If fresh developer makes no difference then the next question to ask is: " how old is your paper?"

I first noticed a problem with out of date paper when I noticed that no matter what my analyser said the contrast should be, the prints all came out looking the same irrespective of what grade I had dialled in on the dichroic head of the enlarger. If your prints all look grey no matter what contrast you use then it could be the paper.

If so, I'd throw it away. There may be ways of salvaging it but the dubious reward may not be worth effort involved. There is nothing more frustrating than trying to produce a silk purse from a sow's ear as the saying goes.