A third. Cost about £15K altogether. We gave them £5K, the in-laws gave them £5K and they forked out £5K themselves. They got about £2.5K in money off friends and family. (As wedding gifts.)
I think it's very uncommon these days for parents to pay for an adult child's wedding, (in full!) and a bit odd. I think it's a bit embarrassing to be in your 20s, (or 30s,) have your own home, and a job, and a partner, and expect your parents to pay for your wedding. Very outdated indeed. Even if you don't expect it, and your parents offer, I still think it's cringeworthy and embarrassing to accept. I don't know a single person whose parents have paid for their wedding in 30 years or more. Me and DH even paid for ours in the early 1990s.
Though my 2 female cousins did have their parents pay for theirs 6-8 years before me. They weren't career women, and professionals like me though. They left school at 16, got a job in a factory, met a man at 17, got engaged 6 months later, and married at 18/19, Had their first baby by 19/20.
They settled down young, but I was more independent and self-sufficient, and took nothing off anyone! I married some years after them. I would never have let my parents pay - OR my DH's parents.
My 2 female cousins mothers (my 2 aunts,) completely took over the whole wedding(s), and invited many people my cousins had never even met... The weddings were basically about my 2 aunts showing off, and both cousins were upset that out of the 80-85 guests, they only knew about 30 people.
Me and DH paying ourselves for ours, meant nobody had a single reason to tell us how our wedding should be. We invited who WE wanted to invite. And DIDN'T invite who we didn't want to invite! There were a few butthurt and very sore people at the time, who never spoke to us again. Result! Never liked them anyway. If we had, they'd have been invited!!!