I know it happens in Australia with minimum bet laws and betting on racing is boosted there as a result. They have to take a bet from anyone at advertised prices to lose $2000 (£1142) on metro meetings and $1000 (£571) on country meetings.
Some bookies seem to offer it in the UK. e.g. sky to win £500 on class 1 or 2 races from 10am.
Betfair also did back here: https://betting.betfair.com/betfair-announcements/whats-new-on-betfair/betfair-sportsbook-launches-500-minimum-bet-to-win-guarantee-on-all-uki-racing-301118-6.html
Not sure if they still do.
Anyone know any other UK bookmakers that take bets like this?
It would be great for racing if the racing channels and racing post etc could push for this at the same time they are questioning the affordability laws. If people cannot bet with the chance of winning where is the incentive for learn about horse racing?