I used to be given luncheon vouchers – does anyone else remember those – as part of my salary as "payment in kind" when I first started working. They had to be declared for tax purposes. Do MPs pay tax on the food and drink subsidies – hell, they don't even pay the bar and restaurant bills, apparently.
The subsidised food in the Houses of Parliament was, I think, established because MPs sat only the late afternoon and evening – sometimes well into the night. (They all had other full-time jobs and businesses during daytime.) It was important to have a place to eat when nearby restaurants, cafés and pubs were closed because it was essential to hear the division bell. (Of course, they could have brought some sandwiches or a plastic container of salad as we all did when we had especially busy or even ordinary days.) Changes to parliamentary hours happened quite a long time ago, so the "need" for subsidised meals and drinks really does not exist any more. More importantly, in these days of food banks as a result of government austerity, it is a slap in the face of many.