I think the attraction of TSA employment is that you're working for the US Government. You get government pay, which admittedly ain't so great, but then you get government employee benefits and, more importantly, get into the government pension system (which I have on good authority is 90% of annual salary and the employee is fully vested after only 5 years of service).

I would also guess that of additional appeal to many Americans, who in general terms are wildly more patriotic and far less cynical than we Brits are, is that they might be doing something for the good of the country.

Is it equally prestigious and/or advantageous to work low-level civil service jobs in the UK? Because if it's not, they you're still only going to attract uneducated, ill motivated, staff even if you were to make security in British airports a subset of one of the security services.