This is an increasingly common practice in the UK for dismissals, especially for reasons of redundancy.
What is going on here is that they are attempting to enter into what until recently was known as a compromise agreement, and is now termed settlement agreement.
Normally, when you are made redundant, you are entitled to statutory redundancy pay (amount depends on age and length of service; see https://www.gov.uk/redundant-your-rights/redundancy-pay). You can take this and do not need to sign anything.
However, sometimes companies make slightly more generous offers in exchange for you agreeing not to take them to tribunal/court or discuss/disclose certain matters. This would often involve more money and an agreed reference. These agreements only have legal standing if you have taken legal advice from a person qualified to give it. The UK's national conciliation and arbitration service ACAS has information on settlement agreements at http://www.acas.org.uk/index.aspx?articleid=4395
Therefore the employer is offering to pay legal fees because they need you to get advice before you sign a document which protects them. They are suggesting solicitors because they know of solicitors willing to do this work for the price they are willing to pay.
Some companies will do this for every dismissal and have a have a standard package for enhanced redundancy. Other companies decide for each case.
Before you proceed to arrange a solicitor, you should check:
- That you are free to choose another solicitor who will do the same for £500.
- That this will be paid whether or not you agree to the terms.
- What your length of service is, what your statutory entitlement is and what the difference is between that and what you are being offered.
You should also think carefully about whether you have any potential claims against the employer - for instance, if you think you are not being made redundant because the employer is doing less of a particular type of work but because you have raised issues of discrimination. You are probably being asked to give up your right to pursue this.
In terms of choice of solicitor, a solicitor which gets work from employer recommendations probably won't be too forthright in encouraging you to challenge unfavourable terms (even if they do not work for employers). If you are a member of a trade union, they will be able to suggest lawyers who do settlement agreements for employees on a regular basis. If not (and I assume not as otherwise they would be helping you through this), I would suggest finding a firm that specialises in representing employees - some solicitors' firms like Thompsons and Morrish are pretty open about their focus.