At my local grosvenor, when you sign in for the day, you get three vouchers.

1. BlackJack -
Get 2-1 odds instead of evens on you winning hand when you place the voucher under your bet.
Max bet £50
Push loses voucher and pushes bet.

2. Roulette-
Get 50-1 odds instead of 35-1 on a winning bet on a single number.
Max bet £10.

3. Slots matchplay-
Put £5 in the slots, they match it with £5.
Some machines you need to play through the £5 once.
Some you can withdraw the £10 straight up.