Why is that so many people seem to think a lack of MOT or Tax means the insurance will not be valid?
As previous posters have said, you have been fairly dealt with..
Had you been pulled over by the police, I'm pretty sure I'm right in saying no MOT is a non-endorseable offence but does attract a fine: had this happened, I'd've expected the garage to do the MOT, pay the fine and make a goodwill gesture, such as the £40 of fuel they've given you.
It was an honest oversight - compensation is not warranted.