The most recent money laundering regulations place such an onus on the lawyer to ensure that they carry out the correct checks prior to acting for a client. Failure to check ID can result in huge fines and in some cases, prison.
In my firm, we use Equifax to carry out the required search, and have a dedicated team who will speak to clients, run through personal details, and will then have a selection of 4 randomly generated 'security' questions. This can range from how many current accounts / credit cards etc do you have; how many times have you missed payments; etc... I find the questions are too intrusive for what basically amounts to a property transaction, however there is also now a requirement from HM Land Registry that the Seller's ID has been verified, and without such confirmation, they will not process a registration.
If a person fails the online test, we will accept two forms of address ID, which can include council tax bill, water bill, shotgun license, benefits letter etc... there are ways around it... but if the lawyer has any concerns, then it is not worth bypassing the checks.