Thames whale - as it happened: Beluga 'Benny' heads further upstream towards London as fears increase

Here’s the media scrum. (They’re actually quite a way from the whale now.)

Update from the RSPCA officers here on site : the whale is moving fairly quickly in the right direction (that is, east and back towards the sea, and away from London.)

Just to put that movement in context, it's gone from the barge you can see here on the left, to around the one you can see on the right – only a movement of 50 metres or so. But it's definitely in the right direction, and at least it's not in the wrong one!

And to put the challenge that awaits Benny into context, too – you can see on this picture some of the river that awaits on the journey eastward. Way off in the distance is the busyness of the London gateway, where ships are arriving and leaving all the time and which is a busy and fairly mucky part of the river.

On this part of the river – where people are being encouraged to watch – there's maybe 40 or 50 people. Most are animal lovers, waiting with long lens cameras and monoculars to catch sight of the whale. The rest are journalists.

When you see Benny, it is only ever in the slightest flash. You'd easily be forgiven for mistaking it for the white crest of the little waves that occasionally break in the water.

Every four minutes or so, it makes its way up and out of the water. Then it'll do that a couple of times more. And then it'll head back down again, swimming until the next time.

Just a little reminder that the whale still being here today is really a little unfortunate – conservationists had hoped that it would be making its way up the Thames and back into the sea by now.

"We are surprised and a little saddened that it has resurfaced again - we had hoped it had gone out to deeper waters and gone out to where it should be," said Lucy Babey, head of science and conservation at the ORCA charity.

"The most likely scenario, which we are not going to know until we can investigate this animal more, is that there is an impairment to its navigation system."

"If that navigation system is impaired or there is a lot of disturbance to its environment, whether from natural causes or man-made noise, the animal will not be able to navigate correctly and can go off course."

This small spot to the right of that barge is the important place – the whale is keeping to a very narrow area there, presumably feeding.

Here – that little white flash that you can hardly see – that's the whale. Look just to the right of the yellow buoy.

According to the RSPCA officials here, the whale will hopefully make its way back when it needs more salty water. That in turn should allow it to make its way home, all being well.