I was recently sent home from my job and a few days later received a letter stating I was suspended for 5 days on full pay pending an investigation for gross misconduct. (A driver where I worked had thrown away 9 boxes of biscuits allegedly on my say so-I denied it as I didn't remember). From the tone of the letter regarding the disciplinary I realised that either way I chose to plead I would be found guilty of the above and I didn't want gross misconduct on my work record so I chose to resign. I handed my letter in personally to one of the managers. A few days later I received a further letter stating that my resignation had been accepted with immediate effect and my final wage and P45 would be mailed out to me on the next pay day. Pay day has since been and gone with no sign of the 5 weeks I am owed and when I emailed the HR department about it they have said I need to have an exit interview with the managing director. This wasn't mentioned in the letter from my immediate manager and I think had I not have mentioned it in an email I would still be waiting to hear something. Can they legally withhold wages for hours/weeks I have worked?

First, you really made an error in resigning, first you can not get unemployment. Second, they are going to give you a bad reference either way, often it is asked were you fired or resign in lieu of being fired. It is not going to make things look any better anyway on a actual background check.

Next you assumed you were to be guilty, even if you told the driver, you live up to it, and suffer a punishmnet, they were putting you on paid leave, so it sounds to me like they were planning on bringing you back. Perhaps a couple week unpaid leave as punishment or a warning in your file. Not that the investigation will not be in your file anyway, with a note that you resigned, really makes you look guility in many ways.

Ok to your question, they are to pay you on the next regular scheduled pay date. So you need to talk to pay roll and find out where your check is