Hi I'm back.
Ok, see he's been dismissed so yes, he needs to get some proper legal advice asap. I also read your other post about needing to fight it and I think the important thing to consider here is what counts as a victory?
From what you've put in your last post I really think there is very little/no evidence to show sex discrimination. Some of this stuff goes back years and is very subjective. That doesn't mean he hasn't been treated horribily (he may have been, we weren't there) and from what you've posted he's probably even been treated unfairly but IMO he's not been discriminated against on grounds of his gender. It could be because the line manager just doesn't like him, and that doesn't count as discrimination. Or he just might not be as good at his job as some of the other people - this is something that can be affected by some of the treatment you've described and his resulting lack of self confidence and attitude. But I'm speculating.
So what you're fighting is an unfair dismissal case. I think your friend (and it must be your friend, I can understand you're angry on his behalf but this is his battle) needs to decide what is a good outcome and what is an acceptable outcome. There is no point fighting to get an apology or tens of thousands of pounds in damages because he is unlikely to get it. Even if he wins an unfair dismissal case at tribunal he will still have to pay all his own legal costs (we're talking around £200 per hour including VAT for a solicitor and £800 per day for a barrister) and unless he has any particular restrictions on getting another job (few jobs in industry, special requirements like part-time/flexible working etc etc) then he will probably get an award of between 2-6 months NET pay. And that's it. Or he might get his old job back.
From putting in an ET1 to a tribunal it can take over year to actually begin the hearing, during which time he will have to show he's mitgated his losses (ie got another job/tried to get another job) which will then affect the level of award made if any.
As his friend I would be wanting to shift his focus from the past to the future. Most people behave with good intentions. That is a fact. He is unlikely to experience such treatment elsewhere. He needs his confidence building and a constructive plan of action to get him another job. Even if he did have to start again at the bottom that has to be better than going back to that organisation?
This is what I would do: Help him find another job. That has to be a priority to help with his confidence and mental health. He may also be depressed now so may need getting to his GP (not everyone will be but he is probably suffering from stress so a GP check up won't hurt).
As part of helping him find another job I would want to help him get the best reference possible, so I would put in a grievance about the way the process has been managed and appeal the dismissal. I would also probably put the claim in to a tribunal - it can always be withdrawn later - but it shows his ex-employer he's serious. Get some legal advice before putting the claim in if you can (not least because it needs to have wording about following the employer's process and that he wants to resolve with employer but has put tribunal claim in to make sure timescale isn't missed), but it sounds like it might be worth doing sooner rather than later.
I suspect this will be resolved with a compromise agreement of some kind. The best victory (imo) would be him getting a new job and his confidence back and from his previous employer a good reference and possibly compensation to cover loss of earnings between old job and new. Anything else is going to be stressful, take a long time and be very, very difficult to achieve.