I've come to the UK not a long ago (March 2019), and back then we had a small team (around 4 people).
The other team members all left, over constant payment delays, so I ended up alone at the office for quite some time. The people that left made complaints to HMRC over possible tax fraud.
Last month, I have received a payment, which was delayed too, and it started to piss me off, so not long after, my boss said this wouldn't happen again, and it did, now.
Yesterday, a brand-new coworker of mine received his salary, but I didn't, so I confronted my boss, and at the end he offered me a pay raise (from 33k to 40k) and a change to my title, but my boss made a change to my contract (probably expecting I wouldn't read it) changing the termination notice period from 1 month to 2 months (coworkers before me all had 1 month, and up until this point I was on probation).
After I angrily confronted him yesterday, he told me he wanted to give me something more than money to show "my value to the company".
Today, I have received an email that I'd receive a part of the salary on Monday, and saying that he wanted to borrow me for 30 minutes on Monday/Tuesday to discuss that "thing he wanted to give me".
I started to fear so I talked with my father and grandfather, and started to wonder what could it be (so I could prepare/arm myself), and we thought that he may be talking about either shares or directorship, which would make sense if someone is in trouble with HMRC or committed tax fraud (even though the company is a Ltd). It's possible that whatever he offers me I will deny: if he can't pay anything on date I can't trust him with anything else, especially with subtle lies and actions.
I want to leave this place as soon as possible, but I have rented a place and I live in a small town, I must stay until October 2019.
I have no clue what to do. If I should leave the company or wait until Monday. Since I'm in the UK since March, I don't know about any laws in here, and I'm really starting to fear that he may be using me. Nobody gets a pay-rise and then receives a new title, salary, and has a "gift" from directorship.