It doesn't look good.
The various RNLI ,police, fire and Hrbmaster boats have been out all day monitoring it and warning off other river traffic. They have got a vet and British Divers Marine Life Rescue trained personnel on board, so they are doing all they can. See http://www.bdmlr.org.uk/pages/main.html
for more details.
There isn't much that can happen until the poor bugger beaches or ceases free swimming. They have a inflatable rig that can support it an allow them to move it through the water, but it is a long way back down river before there is anywhere they can release it.
BDMLR have their own rescue RIBS, so I'd expect them to arrive soon, if not there already. They'll stay with it until they can safely make an intervention, but I wouldn't be surprised if it is a sad outcome.
If it doesn't make it the there will be an autopsy, so we'll know whether it was ill, parasitised or healthy. See: http://www.nhm.ac.uk/nature-online/l...gs//index.html
Fingers crossed that this doesn't happen though. It has been very heartening to see how londoners engage with animals once they know they are there (I admit a 20ft whale does grab attention!). Hope it keeps wildlife in, on and around the Thames on the agenda for a while.