I'm as close to a contract expert as I think I've seen on HPC, being a lawyer who advises on commercial disputes, although tnot property-related ones.
There is the unfair contract terms act (UCTA) and the unfair terms in consumer contracts regulations (UTCCR). This case was brought under the UTCCR.
Basically, under the UTCCR , a consumer is any individual who is acting outside his trade, business or profession.
Under UCTA, an individual or a company is a consumer if the transaction is not integral to their business or a regularly feature.
In UCTA, a business can be a consumer but in the UTCCR it can't.
A property developer flogging a flat would not be a consumer for either of the two (flogging flats is his business);
A cleaning company (perhaps even an estate agent) flogging a flat could be a consumer for UCTA (flogging its own flats is not its business) but could not be for UTCCR (it's a company);
A tv presenter flogging a flat could be a consumer for both UCTA and UTCCR (she's an individual and flogging flats is not her business).
There was a case in which a wealthy lawyer and an engineer who made about 30 forex transactions were found to be acting as consumers despite the number, value and complexity of the transactions, just because it was for their private rather than business purposes. You might say that they used these instruments as we might use a savings account or post office bond. There is no reason why the same reasoning should not apply to those engaged in flat-flogging as a sideline.
The OFT report is here
At this point I can report that Autotrader won't let my father-in-law, whose hobby is buying second cars, driving them for a bit and then selling them to buy a new one (mostly at a loss), advertise as a private seller, purely because of how much he buys and sells, even though it's clearly not a business.