How much ?

[Protagoras]

"The price of stamps has risen again, as the postal service faces criticism for failing to hit delivery targets.
A first class stamp now costs £1.80 - an increase of 10p - while a second class letter has risen by 4p to 91p."

https://www.bbc.co.uk/news/articles/c0mj4mkk94mo

This looks like some sort of demand - price spiral. The price goes up, demand goes down, so the price goes up again to maintain margin at the reduced demand level. Meanwhile, costs go up - more addresses, fuel costs, labour costs.

I'm sure I'm not alone in now sending almost no letters; Christmas cards sent by post are a thing of the past.

Can this even survive as a service?

[tazdevil]

Can this even survive as a service?

No. I think last year was the last we'll be sending Christmas cards which is the only stamped messaging we do.

[ladymuck]

I still send birthday and Christmas cards, although the list of recipients is getting ever shorter.

I used to do postal surveys and got "paid" in stamps. I converted my stash over to the new barcode style and have enough to see me out, I suspect.