A lot of keyboard warriors in here (who I assume are very young) are advising you to go gung-ho, but what you should do is collect evidence, then contact the relevant authorities, only if the evidence you have points to some wrong-doing.
Sadly, I probably can't call myself "very young" anymore, so you're wrong there. Several of us have suggested getting together what evidence they can, but realistically a lot of evidence wont be easy to get. Some statements from employees and ex-employees may be the best they can do. That's why people are suggesting the Inland Revenue. They DO have powers to actually gather that evidence and can be pretty aggressive doing so. The sooner the OP gets them on the employer's tail, the more successful they'll be.
And I don't think "keyboard warriors" is fair. You don't know what people commenting in this thread have or haven't done in their own bad work experiences or encounters with bad / criminal behaviour.
In saying this, the best people to do the reporting are the employees themselves, not a "do gooder", who may not be aware of all the facts.
Sound advice if the OP were a judge in the case, but they're not appointed to determine innocence or guilt, they're talking about making the people who do that aware of what is going on. Honestly, I wish we had a few more "do gooders" around. Most people turn a blind eye to wrong-doing.
There are ALWAYS 2 sides to every story and you should first hear the employer's side of the story, as part of your evidence gathering.
They have been told about the situation by their friends and people they know. That seems to be sufficient to them to believe this is happening. Again, you are putting the OP in the role of prosecution. They are not and they are not trying to be. They're in the role of sounding the alarm. I've seen work circumstances like this. They're not good and being told by people you know in that circumstances is enough for one to believe it. What other side to the story do you expect from things like months without pay or excessive working hours? You can hardly expect the OP to go to the employer and say "I'm thinking of shopping you to the authorities, but I wanted to hear counter-evidence first." Be realistic.
Given that these young workers are working 48+ hours per week, makes me think that things can't be as bad as things are being made out.
Isn't working 48+ hours per week a sign that things are? I mean I've worked much longer hours than that for periods but still, few young people raised in the UK are going to be doing that without pressure to do so.
I mean think logically here, if I have not been paid for 2-3 months, why would I then put in a 48 hour week? I wouldn't even turn up to work! The story of the bad empoyer makes no sense at all.
Firstly, it doesn't have to be the same people in both anecdotes - some people are putting in 48+ hours per week. Some people haven't been paid for over two months. Could be different people - it's your assumption that they're not. But I'm also going to point out that it's very plausible. Maybe you wouldn't turn up for work, but a lot of people will so long as they're promised "sorry - lost your timesheet / didn't seem to go through / missed this month's because of when you started / you have to work a month in advance here / I'll make sure you get it next month". You'll find plenty of people who'll stick it out
especially if they've already done the work and think quitting might mean they don't get the two months back pay they're already owed. Been there, heard it all before and was promised the t-shirt any day now. Honestly, for someone calling other's "keyboard warriors" I suspect you don't have a lot of recent experience with that sort of working environment. There are
always people you can take advantage of. It's exclusive to the unskilled / young labour market either - I've seen more than one senior manager who continued to throw money at a busted project because of how much they'd already invested. Same principle - you're owed two month's pay and have been fed two semi-plausible excuses (one for each month). Do you jeopardize all that money by walking? Maybe you will, but you're not in the situation many of these people are and don't have their perspective or career background, probably.
I honestly see no good reasons to doubt the OP's story or even reasons why they should discount what people they know tell them is the case.