@Ian H I've been a long time member here but very seldom post anymore but your plight made me post.
Companies nowadays are tightening belts, whilst I understand that you are effectively paying for a breakfast you could of had at home and a dinner you should be eating at home you aren't technically working away.
If I have read it right, you are being paid from door to door regardless of start and finish time (correct me if I'm wrong?) As such the additional cost of a breakfast or evening meal/snack for dinner is already built into your hourly rate. If you had to stay over a night then I would say that you are more than entitled to a meal allowance but as its a "normal" working day then then it isn't payable.
The above assumes that none of this is written in your contract of employment. If it is stated that before a certain start time you are entitled to an allowance for breakfast and if your job takes you past a certain finish time you are entitled to a dinner allowance and they have failed to give you 30 days notice to a change of contract then you are well within your rights to challenge it.
If, however, it was just a gentleman's agreement that you could charge them your reasonable expenses and they have now decided to change that then I don't think you have much to stand on as it was, as you said, a perk.
If you are working away then you are allowed an allowance and can offset it against tax payable. You need to be "working away" though to claim this.
From your previous posts I've read you seem to enjoy your job and you obviously have a good line of communication with your boss/bosses. I'd be inclined to have a friendly chat with them to come to a mutual conclusion and try not to upset the applecart for what is effectively about a fiver a day.
If your in Tamworth again I'll hook you up with the best breakfast in town and I'll get me mother to make you a dinner! I'll even ask her to do you a receipt!
Failing all of the above then just PTLB of your gaffer. Jobs a guddun!
Jon
Edits for poor spelling and grammer