How do the PM, Secretaries of State and the Speaker of the House of Commons help their constituents?

Question

The Prime Minister, Secretaries of State and the Speaker of the House of Commons seem to represent their former constituency even after they become speaker. For example, the current Speaker, John Bercow, is still the representative for Buckingham.

Do constituents in those districts have the possibility of going to surgeries like constituents of other districts do? If so, are those held by those holding the aforementioned positions or does another MP take over?

A quick search lead me to the following quote on the website of the UK Parliament:

What if my MP is a Minister, Speaker or Deputy Speaker?

If your MP becomes a government minister, the Speaker or one of their deputies, they are still able to help with problems that affect their constituents. They will, though, use other methods instead of raising issues publicly in the Chamber.

Unfortunately, it does not provide much detail as to the specifics of those methods. Can anyone elaborate on those methods?

Answer 1

These other methods may include sending letters to the relevant government minister, discussing in (or outside of) cabinet, or other informal meetings.

In the past, whenever I have written to my MP on an issue (who is neither Speaker nor Minister), he has followed up with a letter to the relevant government minister, and forward said minister's reply to me.