just to add it is perfectly possible there is a confidentiality clause as part of his contract which would prevent him speaking to people after dismissal - as has been said taking laptop/phone etc straight away is common and fair enough especially in sales, and the not talking to people is likely to be for a similar reason - not getting info about clients which he could use/not poaching staff as well.
If you appeal something like this usually the easiest and most successful way of doing it is by stating that the employer didn't follow the correct procedure - it's so common for employers not to follow it properly as chockimmy said, and obviously easier to prove to an appeal hearing or tribunal than 'what they said about me was wrong'.
Sounds as though they did follow a reasonable procedure though, so if your DH wants to appeal it he would have to do so on the basis that the targets he was set for improving his performance were unrealistic and he wasn't provided with adequate support to do his job properly, particularly as you say he did raise this regularly at review meetings.
Instinct is to fight back, but appealing on the basis of something like that will be very tricky and I think may be unlikely to lead to a different decision, fair or not. It sounds like they want rid of him and have been careful to go by the book to do it.
You could certainly put together an appeal based on those things, attacking not the procedure but the 'reasonableness' of their decisions and of their management of him, and it is possible the decision would be reversed by whoever heard the appeal.
However, if he does that, things to think about
- Make sure he takes a union rep or colleague to the appeal meeting
- This has happened because they want rid of him. If his dismissal is overturned, he will probably be put on a final warning instead, and if he puts a single foot remotely wrong in the next 6 months or however long is set, he will definitely be out, and as they want him out they are likely to engineer it (only more carefully) to make sure this happens. So it is likely to be delaying the inevitable.
- If he appeals it, and fails, his next step is to take it to a tribunal. I would say it is unlikely that doing this would be financially worthwhile for a case like this where procedure has been followed, it would be extremely difficult to prove and his award even if successful probably wouldn't be worth the hassle tbh.
- If his employers were the kind who were likely to pay him off rather than go through a long drawn out performance management process, they would have done it by now, so they are more likely to just delay it if an appeal is successful rather than chuck some cash at him to leave quietly.
(This is getting longwinded!). I have said this before and I always say it, best thing to do in any circumstance like this is take a minute to calm down, as first instinct is anger and an urge to fight. Then think about what outcome is best for your DH and you. Not what is fair or right, but what would be best for you. And then think how you can get there. Best outcome for your DH might not be to have his job back, even if it's unfair how he lost it. Only you and DH will know that, but these are some points to think about.
Rightly or wrongly, however badly an employer has behaved, it's not always about punishing them. Sometimes it is, but sometimes it's better for the individual to look at their personal circumstances and how this affects them and decide what would make them happiest, and that's not always what would be seen as 'justice'. As I say, up to your DH. If he does want his job back, at least to give him enough time to find something else so he can resign before being sacked again, it might be worth bunging an appeal in based on the things mentioned above, it might be successful, and if it means he can find himself something else and then resign head held high, that might well be worth it.