I went to a charity shop* to pick up a black jacket when the FIL dies earlier this year. Cost me £15 for a suit. Double breasted so not fashionable** but who cares at a funeral as long as it’s respectfull and fits.
Plenty of people don’t own suits so come in coats, fleeces, jumpers, allsorts. I don’t think anyone would be bothered as long as you made an effort to be respectful to whatever the family wanted.
*being a charity shop I appreciated the irony of potentially buying a dead mans suit for a funeral. I’m a serial charity shopper though, my black-tie outfit for last years christmas doo was a £1 DJ from a charity shop, ditto shoes and waistocat, black flat-front office trousers from M&S, braces from Matalan! Black tie for less than the first round of drinks cost!
** If I keep it 20 years it’ll come round again.