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...unless the beeb is allowed to have ads on it.
In my opinion a bbc search engine would have to offer something that the other search engines can't provide to justify its existence (as we're paying for the bbc) - otherwise why should we pay for something that others (google etc) already do fine? I have no idea what they could offer that others don't (then again bbc news is arguable the worlds best news site, so perhaps I shouldn't be quick to judge).
The beeb are also actively looking to cut back on their websites just now, so it seems strange to start looking into producing a search engine.
For example, pick up a copy of Top Gear magazine or Gardener's World (any magazine by the BBC) and you will see adverts in them.
They may be able to display ads on their search engine.
Usage has been relatively low, and I don't suppose it would be very different if they made their own crawler - the end users wouldn't really know the difference.
I would welcome another crawler based engine though; that can only be good news.