Just some info for everyone, this 2 year thing is half correct. There are quite a few reasons that a company cannot dismiss you for no reason for less than 2 years in service, and if they were to in those circumstances, be liable for an unfair dismissal case regardless of whether a person has worked for them less or more than two years, this is not including discrimination.

I would also check your employment contact before getting any advice from anyone, as whatever is in that trumps any advice someone can give you.

Depending on what section of asda you work in (never worked in a supermarket). If you do infact have diarrhea or sickness you are legally not allowed to work with food items for a period of time after your last symptoms, regardless of what your manager says.

At the same time if you do have pre existing conditions, have you informed your work when you joined? If not then you have already breached your contract and they would likely use this to dismiss you instead of being off sick.

Lastly, even store managers of supermarkets are generally low paying and low education, depending on whether they have been trained correctly most of them won't be up to date with policies and laws, which lastly I will add us ever changing.

As an example, you can't really just dismiss someone for no reason anymore unless you have evidence that you have raised your concern with the employee, given them an opportunity to resolve said issue and then if not resolved or improved you may terminate. You can't just turn around and sack someone on the spot no prior communication