Hotels are expensive; hotel room minibars are the worst of the lot.
However charging UKP2.50 for a standard can of Pepsi does seem excessive. Way over 400% markup. For US readers that’s a $5 can of Pepsi.
Most US Marriott hotels have 24 hour vending; I can go get a can of Pepsi for maybe $0.75.
The London Heathrow Marriott gets this trips award for the biggest ripoff.