When you write to your MP keep it as short as possible. Actually if someone could write a catch all draft and post it here and on the Publican website that would be a good start. Maybe that's too much to ask...
Anyway. When I've written to my MP's before (Harriet Harman and Kate Hoey) they have always responded directly when it's been something to do with me or the local authority but have to pass it on for an official answer when it's outside their remit of experience.
When it's passed on it always gets bogged down in mandarin bureaucracy no one writing back to an MP is going to write anything that has a come back and leads to more work. The official line is always "blah blah blah" "quote quote quote" "hope that satisfies the gnome asking the question" nothing ever answers the question directly. This is just a part of politics.
The way around it is to immediately respond courteously that the initial question has not been addressed or if it ahs - to ask for the answer to be backed up with direct evidence. They must respond. So make it as tough as possible. It all takes time though and that's what most people don't have.
You have to understand that when an individual gets in touch with an MP and that query goes up the line, it's just an irritation placed by one lonely individual that's not supported evidentially by anyone else - just an isolated niggle. Politicians are constantly bombarded by time wasters with useless demands that are time consuming and ultimately fruitless if they are followed up. This is why the democratic system has evolved to protect itself from endless time and money gobbling investigations on behalf of every individual that ever writes to an MP.
This is why you must expect a long, obscure reply that appears erudite and baffling and seems to deal with what you're asking about but actually tells you nothing.
Expect that and when you open the letter it won't be bewildering and you'll be able to keep calm and write a brief note back saying 'thank you for your response, much appreciated but you have not answered... the question I asked' and get it back to them asap. You will make progress. Ask your nearest other publican to write and ask the same question. Logical, boring but necessary..