Many of these accounts are umbrella accounts. Also called customers' reserves. Here wines will be stored under customers' names but will be part of an umbrella account held by the wine company. This is a popular arrangement for both legitimate and less legitimate companies as the customer doesn't have the hassle of setting up their own account. However, this arrangement does have the serious drawback that the wine company can move wine out of your account without your permission and knowledge. Furthermore the bonded warehouse naturally takes instructions from the account holder – the wine company.
My advice is to open your own account with a bonded warehouse. This way you have full control over your wine. There are links to some storage companies on the right hand side of this site.
There is nothing to stop a company selling you some wine, putting it into an umbrella account at one of the UK leading bonded warehouses and perhaps inviting you to check with the bonded warehouse that your wine is safely in customers' reserves. Once you are reassured the company might decide to remove your wine and either sell it without your permission and pocket the proceeds. Alternatively they might create a new company and move your wine into a new account set up in the new company name with no indication that this was once your wine. It is quite likely that you would not become concerned until you either decided to sell your wine or if the initial company disappears and you become concerned as you cannot contact them. By which time it is, of course, too late as your wine has disappeared along probably with the people running the scam.
I understand from a reliable source that the Metropolitan police are currently looking at around 20 wine investment companies.