Re: Still do not understand
>"I believe at least some banks let you pay in a check by uploading a photograph,"
I'm using Starling bank, at present they will take (endorsed) cheques sent to a freepost address but are developing a feature such that you just need to send a photo of the cheque using their mobile app.
Getting cash - use the Cashback option at a retailer or post office.
Paying in cash is harder, easier is to just spend it! however that is a problem for businesses taking a lot of cash payments - market traders perhaps. I think some banks have a deal with the post office to take cash - for a fee.