What makes me almost certain that Smith Associates is part of Humphs empire, is because it's registered as 'Unlimited', which is very, very rare - and is the same as the main Sam's company, which was status changed from 'Limited' to 'Unlimited' when investigations were in process for the Times Rich List - the same time they then removed all external brewery title livery.
The main differences in status are that whereas a Limited company enjoys limited liability (Directors not liable for finances, with a few legal exceptions such as law breaking and indemnities), an Unlimited company usually has all shareholders personally liable for any company debts.
Bare in mind, a company of either status registered at companies house, is still an entity on it's own, and should be run in accordance to English company law. For example, you can't knowingly destroy the company.
Another main difference - and this would appear why the change was made - whilst Limited company's details (accounts, returns, shareholders info., and articles) are publicly available form Companies House for a small fee, an Unlimited companies details remain out of the public domain.
Speaking of limited companies, I noticed that Lincoln's Widows Cullen Well, is in some places listed as a Limited company, as can be seen
here - 'Widow Cullens Well (Tadcaster) Ltd.', which is a bit strange, as no such company is registered at Companies House - if it is a Limited company, it could be registered in another country.