Would definitely recommend using a solicitor specialising in wills and probate. I believe it is penny wise pound foolish otherwise, particularly in relation to the inheritance tax planning aspect of it.
The nil rate band (amount that is exempt from inheritance tax) is currently 275K pound sterling. The value of your estate that exceeds that amount will attract inheritance tax of 40%. It is easy for the combined value of a couple's estate to exceed 275K if you add up the value of property at today's prices and proceeds of any life insurance. You could potentially save thousands in inheritance tax compared to the 375 pounds I paid for a solicitor to draft a tax planning mirror will.
The Tescos will pack I initially bought to save myself that sum would not have got me very far in hindsight!