£25 cashback. Applicable to customers who apply for an HSBC 32 Month Balance Transfer Credit Card between 14 May and 16 July 2018 and use it for either purchases or a balance transfer (fee applies) with a minimum value of £300 within 60 days of account opening. Terms and conditions apply
https://www.hsbc.co.uk/credit-cards/
First Direct regularly run similar promotions too, although their current offer is only £20 cashback for £1500 spending.