TechCrunch reports that Bebo has spurned the advances of UK telecoms behemoth BT, which is rumoured to have offered more than £300m ($552m) for the social networking site.

However, a senior BT executive told E-consultancy that this is nonsense.

Our BT source said: “We can state categorically that BT has not had any discussions with, or made any approach to, Bebo. We’re not sure where this rumour came from.”

UPDATE: Bebo’s Xochi Birch also emailed me to say: “BT has not approached us and we currently have no contact with anyone at BT.” She also has no clue about where the rumour came from.

It also makes us wonder exactly where the rumour came from, and perhaps more importantly, why it started in the first place.

Bebo recently attracted investment from Benchmark Capital, a savvy tech investor, which ploughed $15m into the fast-rising social networking site.

Interestingly, Benchmark didn’t deny that Bebo had been approached by BT, when asked for clarification by Michael Arrington.

A Benchmark spokesman told him that “there has been a lot of interest from a lot of people around Bebo”. Those are certainly the right noises to make if you’re angling for an exit / encouraging offers.

Bebo’s growth, like rival MySpace, has been something of a phenomenon. It must have racked up some fairly sizeable infrastructure costs, with the 3 billion page impressions it serves up every month. Presumably Bebo hasn’t spent all of that $15m already?

Now is probably not the time to get into the nuts and bolts of Bebo’s business model (current or prospective), nor concerns over the longevity of its active users (youths tend to be fickle and fad-orientated). Let’s save all that for another post.

However, I think it is safe to say that had Bebo rejected a £300m offer, Web 2.0 would have jumped the shark.