Not sure what you should do but this question is literally the reaosn why I did not apply to them last year. I think it's really private and a very weird thing to ask. People can, for example, go to counselling for a variety of reasons and I don't think firms are entitled to know every little bit of your private life.
Anyway just a rant.
Regarding the "lying", applications usually have a statement at the end saying that you acknowledge that everything you said was true so not sure whether they could do anything if they learnt you lied... although quite unlikely they would unless you told them later
It's slightly ambiguous, but in my view
"Have you ever required any treatment or counselling, or been the subject of any disciplinary action by an employer, relating to alcohol, drugs or gambling?"
Means
- Have you ever required any treatment or counselling for either alcohol, drugs, or gambling or
- Have you ever been subject to disciplinary action for alcohol, drugs or gambling.
They're not asking if you've had counselling for anything else - depression, relationship issues, etc.
So if you have not had treatment/counselling for one of those things, but have had treatment/counselling for something, else you should answer no.
There is also a "give details", so it's not disqualifying.
Note
https://www.legislation.gov.uk/ukpga/2010/15/section/60
1)A person (A) to whom an application for work is made must not ask about the health of the applicant (B)—
(a)before offering work to B, or
(b)where A is not in a position to offer work to B, before including B in a pool of applicants from whom A intends (when in a position to do so) to select a person to whom to offer work.
There are exceptions, but for example, a person who is a "high-functioning alcoholic" (i.e. who has not got into trouble at work) and who has been successfully treated for that, is of no relevance to the firm at all, so this question does appear unlawful.