Will Bank also look at the Joint Bank Account when making Single mortgage application

Pkwesi

I have recently managed to get a mortgage in Principle with HSBC to port my existing mortgage as well as borrow additional amount on top to buy a new proprety.
when making the application, they asked me for my outgoings which I listed but then some of these are paid for by my boyfriend from his bank account. They told me i still have to list it which I found strange.
Anyway the rest of the monthly expenses such as council tax, gas etc ... are paid out a joint account that we have. Every month we transfer a set amount, say £250 each into that joint account which covers all the household expenses. I have a bank account in my name only as well. I know I have to submit my bank statement to HSBC to get a formal offer but this statement will not show any household expenses going through, just £250 out to the joint account. I was just wondering whether HSBC can / will demand that I include the joint account bank statements as well, as supporting documents before they will give me a formal offer? But then this bank statement is in my name and boyfriend. can they do that?
Have anyone had any experience of this that they can please advise me?