Radio 4 current have a story on this on You and Yours and people are being asked to report this to Trading Standards. It's where they're not passing on an offer made on a house UNLESS you sell their house with them or use their in-house brokers.
I think there's a slant on this in that if you're chain free and already have a DIP your offer isn't being put forward. I can attest to this having three times in the past been surprised that my offer hasn't been accepted and gone to the Vendor to ask why and been asked "what offer?". Apparently there's a petition to have the EA's regulated and I wholeheartedly support it.