I'm aware of a number of places in South Australia (e.g. large shopping complexes) which do specifically include cleaning costs in their lease agreements for places selling food in disposable wrappers, but that's always a private arrangement at the discretion of centre management. Station operators could consider doing this, with incentives for food retailers which have a low proportion of their wrappers found in random litter surveys.
Has the responsibility (or lack of) held by a food retailer for what happens to "their" wrappers once sold been tested in court in England yet?
I don't think a tax would work. It would be too hard to enforce, unfair to places that have a high proportion of people eating inside their premises (and therefore discarding or disposing of the wrapper there as well) and probably an overall loss-making exercise for everybody. It also wouldn't do anything to address the problem at its root - public attitudes to littering.
A sustained PR/education campaign trying to change public behaviour would be better. There are many ways this could work, one that's popular and relatively effective in Australia is the yearly regional, state and national "tidiest town" awards which work by engaging the same local pride that normally goes into local sporting teams.
I even know of two neighbouring towns (neighbouring = 50km apart in this case) which integrated this into their humorous annual competition for the WAAC Trophy (Win At All Costs) - contested in football and cricket by the men's teams, netball and hockey by the women's teams, and the higher ranking in the regional tidiest town awards as the fifth event. It occasionally has the odd effect of making the tidiest town contest a bigger event (and therefore subject to more cheating and taunts in the local papers) than any of the four sports were, such as the year one town had a useless footy team so they bribed (with beer, of course) the judge to look at the other place the morning after the whole town had partied hard over the football win, the place was a mess so they ranked lowest in the tidiest town competition and lost the WAAC Trophy.
For pre-packaged drinks in cans, bottles or cartons, a container deposit scheme works well in South Australia for general litter reduction in public places. A deposit of 10 cents is paid to the government by the manufacturer/importer and included in the retail price of a pre-packaged drink sold in SA, and if you choose you can collect a refund when you hand it in at a recycling depot. The main purpose of the scheme is litter reduction, and to see that it works you just need to drive over the state border and see the difference in the cleanliness of public places with far fewer drink containers and plastic bags lying around (it's illegal for shops to supply plastic carry bags free of charge at the checkout, you need to pay).
It's not a huge amount of money (it's about 2-7% extra on a discretionary purchase) but it's enough of an incentive for socially marginalised people and community groups like churches who can make a decent amount of money off collecting thousands of discarded cans/bottles/cartons while also helping keep public places clean.
Just for a bit of trivia, South Australia is the only place in the world where a milk drink - Farmers Union Iced Coffee - outsells Coke, which even drove Coca-Cola to launch their own milk drink range which tasted terrible and tanked badly when retailers refused to stock it.
The container deposit label is circled at the bottom. The photo is mine, but unfortunately that particular carton of FUIC was not.