You can google the ACAS site and gov.uk to understand the process companies must follow when they’re making people redundant. You can also check the legal minimum for redundancy pay (it’s based on age and years of service)
Most companies will offer a settlement agreement whereby they pay you above the legal minimum in exchange for you signing away your right to sue them at an employment tribunal. This allows them to short circuit the redundancy process.
However, by law, your agreement not to sue is not enforceable unless you had qualified legal advice before you agreed. In other words, you must have a solicitor review the agreement and explain what it means. Often companies will pay all or part of the cost of a solicitor as it’s in their interest to have the agreement hold.
If you do think the redundancy process hasn’t been followed correctly, then you or your solicitor can raise that with the company. At the end of the day, it’s a negotiation. Also, remember it’s not just about salary. You can also negotiate regarding bonus, options, pension contributions, and notice periods.
Keep in minds, you’ll need to be able to prove the process was a shame and be specific about what hasn’t been done correctly.
Keep notes with dates and times on every conversation you have. Ask questions in writing about the process and make sure the answers follow the law. Don’t be afraid to call out when the process isn’t being followed. If a company is told they aren’t following the law and don’t correct, that will likely look worse for them.