26 hr Layover at London Heathrow (Transiting)

My dad is travelling from Cayman Island to London Heathrow on may 6 arriving at terminal 5. He has a lay over for 26 hours and has a next flight going to Qatar, then Qatar to Philippines.

I’ve read and research that the airside are not open 24 hrs so no matter what it takes he has step out & find somewhere to stay like hotels nearby the airport. To be able to do it he need to obtain a transit visa right? Can a transit visa be granted in the airport or at border control?