Hello Richard my name is ***** ***** I will help you with this.
Have the insurance company said why its so short in terms of payment please?
You don't have to accept the offer and indeed you can accept it as part payment, unless it says in full and final settlement. if so you should not accept this.
You should also write a letter of complaint to the firm and set out your reasons why they got it wrong. This will be investigated and they will come back to you with a response.
If you are not satisfied with the response at that point you can complain to the Ombudsman. They offer a free, independent service and can investigate your complaint at: http://www.financial-ombudsman.org.uk/
But to answer your questions - you do not have to accept the £4,300. Its a commercial decision for them to offer less, its not against the law.
Can I clarify anything for you about this today please Richard?
All the best. If this answers your question could I invite you to rate my answer before you go today, otherwise the site doesn’t pay me for the time spent with you. Thanks in advance and good luck.