I'm a property lawyer and may be biased haha but I wouldn't recommend anyone doing their own conveyancing unless they really know what they're doing especially with a lease!
Is he getting a mortgage? If this is the case I can't imagine the lender would accept it and would insist on using their own solicitors/legal advisors to protect their own interest. I this case he would be best off instructing solicitors who can act for the lender as a part of the conveyancing.
In any event, he may have a book telling him the process but does he know how to interpret the searches (and what searches to do if required over and above the standard), replies to enquiries (and even what enquiries to raise and what to question further), title documents and plans, other side's solicitor's correspondence and everything else. What about if other aspects are involved such as a sale by executor, if assents are involved or say the Court of Protection or trusts, charities, companies etc..., if anything could invoke the provisions of the Insolvency Act.
Would he know how to draft any additional clauses or documentation needed so they protect him properly? Could he spot and issue with boundaries which could lead to a costly dispute or decrease in valuation?
Would he know how to protect himself from any issues such as fraud (including mortgage fraud) or money laundering?
Does he know what should or shouldn't be in any contract or transfer (and if something should be in there how to draft it), the difference between standard and special conditions, the source of the standard conditions and which version is to be used and their effect.