Put a return address on the envelope so it gets returned to you if it doesn't work, then you'd know

Thanks Lorraine..and I know what you mean, it takes about 4 or 5 stamps just to make 80p worth of value

Hey there, as far as I know they should still be good to use, you may need to stick on more though just to make up 'today's value', but I'd give it a go & see if you get them back

Good luck!

Thanks Andy, they're all in mint condition so I'll give them a go and see what happens..

If they've never been used, then yes, I think they're fine to use, as long as they cover the required postage.

My father just bought me well over a hundred mint British stamps from the 1980s & 90s. Apart from the ones I'm going to keep for my collection, he said I can still use the duplicates for return postage when sending autograph requests, even though they're not current. Is this true? Thanks.