You'll have to look at the terms of the particular pension. In my case if my widow even cohabits, let alone re-marries, she'll lose my pension (Civil Service). Similarly if I cohabit as a widower I'll lose my wife's pension (private company). All pensions may not be the same.
My mum was widowed and my dad's firm still pays her his pension even though she has remarried. It will depend on the terms and conditions as others have said.
soapnumpty ^^ it also depends on if she has told them she has remarried.
I know of a case where the lady is still claiming her late husbands pension despite having remarried, she knows it would stop if they knew but she is just taking the risk. She says '' I'm not going to tell them and I can't give it back once I've spent it''