Employer is trying to stop me working for 6 months due to

Thank you for the for the clarification, it is common for employment contracts to contain post-termination restrictive covenants. However, a covenant that restricts an employee's post-termination activities will be automatically unenforceable by being in restraint of trade, unless the employer can show that it was there to protect a legitimate business interest and did so in a reasonable way.

The courts try and balance the interests of the employer's business and the employee’s right to freedom of movement and earning a living. Such covenants will generally only be reasonable if in the process of working in competition, the employee has access to sensitive confidential information or they have influence over clients is so great that such a restriction is necessary.

Restrictive covenants are often used as a scare tactic by employers, however whether they are enforceable will often need to be decided by a court.

Yes the courts will often view restrictive covenants on a case by case basis. Yes you could use a solicitor to respond to the letter if you wish. From experience I have seen several letter such as the attached, however it is rare for a company to pursue legal action because of the length of time and significant costs involved.