Sign up to Mettle (it's a business account but can be used for any side busses too like your eBay sales or cottage industries). Once it's all signed up, make one card transaction and then add the code in the app under Account > Redeem code. ยฃ50 cash is added to your account next day.
1. Download the app from your app store
2. Complete sign up using referral code: UTHDNFUA
3. Link a current account (this can be any account, doesn't have to be same account as mortgage)
4. Complete signup (contact, address etc.) and they will find your mortgage account automatically
5. Set up direct debit (ยฃ25 is the lowest amount but you can cancel once you've got the bonus)
6. If you're after the money quickly, do a quick ยฃ5 top-up and then ยฃ20 bonus is added in a hour or so. You can then either withdraw the full cash immediately (or send it to your lender to knock a bit off your mortgage)