What appears to be an offshore rig equipped with an enormous crane has appeared in the Mersey. At least it looks like its in the river from where I saw it but it could be in one of the docks.

Anyone have any idea what it is and what its doing there?

Could it be the Vidar Semi submersible
http://www.4coffshore.com/windfarms/vessel-vidar-vid608.html

Its on location here on the Burbo Bank wind farm extension ..
http://www.burbobankextension.co.uk/en

I was in Victoria Park early this morning could see it lit up.Heared something about it on the radio but was busy getting kids off to school so didn't quite catch what it was there for

Looks very like the Vidar.

It is the Vidar :-
http://www.liverpoolecho.co.uk/news/liverpool-news/massive-140m-ship-arrives-liverpool-10768000

Dave