Interest is crippling.
I know a chap who did the whole 3 months.
His bank told him he owes an additional 3k on top of his original mortgage amount for doing it.
He only skipped 3* 850 payments and owes an additional 3k plus the 3 payments he missed.
Martin from that money website goes into detail about why its a very bad thing to do.
Just to crunch these numbers, (using simplified maths, it doesn't quite work like this).
£850 x 3 = £2,550
Assuming you return to normal payments, a holiday will mean your mortgage is £2,550 higher for its entire duration, compared with not holidaying.
That means interest on £2,550 every year until you pay it off.
At 3% interest (higher than present rates, but perhaps a better long-term estimate):
£2,550 x 0.03 = £76.50 per year
Assume it's a pretty new mortgage, so 25 years to run:
£76.50 x 25 = £1912.50
So your £3k figure isn't too wild (has he got a really long mortgage, or a crap rate?). But for a lot of lenders you'd pay that extra over the full term with slightly increased monthly payments:
£1912.50 ÷ 25 years ÷ 12 months = £6.38 per month extra
And for others, you'd just pay an extra few months of mortgage at the end, a long way in the future.
It's certainly worth taking a mortgage holiday in the present if your finances are very tight. Most people have a shorter term than those calculations, so the extra interest would be much less and, therefore, the holiday would cost even less.
It's certainly not 'ridiculous' or 'bonkers' to take the payment holiday, even if you don't actually really need it. Though I would suggest people don't unless it's necessary.