That's precisely it Factor.
The contract between a solicitor and a client only provides the client with redress in breach of contract or concurrently in negligence. English law does not recognise a breach of contract being able to provide damages for a third party (apart from the Contracts (RIghts of Third Parties) Act 1999 which does not cover this area). When White v Jones went to Court their Lordships (on a majority - not unanimously) decided that this lacuna in the law needed addressing - although it was somewhat ironic that their lordships who were all of a similar age to the testator took several months to deliver their judgement, but I digress......
Anyway, it was decided that - subject to the retainer - the solicitor owed a duty of care to a beneficiariy who was disappointed as a result of their negligence. The lacuna to be addressed was the fact that technically, only the executors had a cause of action against the negligent draftsman but of course, the "estate" hadn't lost, but potential beneficiaries had.
Other examples include:-
Failure to advise testatrix to sever joint tenancy on making a will - Carr Glyn v Frearsons
Failure to ensure that the will was properly executed - Esterhuizen v Allied Dunbar
There are some good lecture notes here:-
http://tenoldsquare.c...ce%20in%20Probate.pdf
Absolutely fascinating area though.