Yeah, there should be one.

Just because food is expensive or perceived to be high-end doesn't necessarily mean it's healthier anyway - I imagine plenty of people who delight in turning their noses up at McDonalds would be shocked to know their large Mocha with cream from Starbucks contains as many calories as a Big Mac.

T5 has numerous food outlets where you'll pay £8 for a meal that still isn't particularly good. Don't think there would be any harm in one low-end / budget operator, without turning it into a US airport. Besides, McDonalds is an unsurpassed hangover remedy

In reality it would be more likely to be Burger King as they don't maintain consistent prices nationwide and have lots of more expensive services stations. McDonalds, as far as I know, don't.