If you are only asking, they don't really need any papers (at least when I did it) as they will be "informally" asking about your income. If you want to make an application, as they will need proof, then you need:
6 months bank statements (your and your partner if joint mortage)
P60 (both you and your parner if applicable)
3-6 months payslips
Bank should provide you with an application form your employer will have to fill with some details.
If you have any outstanding loan, they will also require statements for this, to calculate the outstanding balance, term, etc.
Photo Id
Proof of address (utility bill, etc)
If you are applying for a 100% mortgage (i think I read you were), one of you have to be in FTE for 3 or more years and at least 1 year for the other.
As I was changing jobs when applied, my broker said they wouldn't even consider our application, but when we went to the bank, because it's a more personalised service, they didn't have a problem giving it to us, as the mortgage advisor there "pitched" our case really well, making us look good (not that we are not good enough , mind you). I reckon it's good to go to your bank, as they should have a lot information about you already, if you are a good costumer, etc.