I've done the route with BA a few times and can vouch that since the introduction of the M&S menu, it can be a slow process for the trollies. Usually 3 of the 4 crew work economy so I think they're doing the best they can but it seems their payment taking is not up to speed. Top tip is to order a hot item when they take pre-orders and at the same time they'll usually take the rest of your order so you don't have to wait for the trolley to reach you.
I was on a easyJet flight a month or so ago and by row 4 they'd run out of hot food and I do like their ham & cheese melt
In terms of Liverpool flights with EJ, been and done about 4 years ago so would be surprised to see them return although with less competition down the road in MAN, maybe its a good time to try?