There is an extradition treaty between the uk and us....so if someone commits a crime in the UK and is in the US, they can be arrested in the US and extradited. This has existed for forever and is between many countries...so yes, technically the UK could have the US extradite citizens to face charges in the UK.
The odds of meme posting being serious enough? Slim to none but with the batshit crazy governments we have these days, I'm not as hopeful. It also has to go through the local judicial system and get executive sign off (secretary of state I think in your case), so maybe a couple token people get shipped over, but no way they get more than that.