Yes. Large white butterfly larvae - people use nasturtiums as sacrificial plants to attract the adults away from their brassicas.

The black bits are caterpillar poo!

Large cabbage white, if memory serves it's Pieris brassicae . Used to be one to study at O'level back in the 70's.
their eggs are yellow, long cylinders and you always find them under the leaf.

They look like tent caterpillars - they are highly social and highly destructive & will defoliate everything.

One of them has turned into a chrysalis on the wall behind our loo in the bathroom!

They are definitely not tent caterpillars and these are easy to identify as cabbage whites Bathgate. Tent caterpillars are a real problem here too especially at one of our local beauty spots.

I'm not so sure about that Sea- Cabbage Whites have yellow eggs. If you go back and read the post, the eggs here are black. Also these are Nasturtiums, not cabbages. Cabbage Whites like cabbage plants. They look like tent caterpillars.

They love nasturtiums too Paul. They are the most common one seen in our gardens and can destroy both brassicas and nasturtiums very quickly. They do not leave webbing at all.

The eggs are different too

the black eggs were assumed to be the caterpillar frass on the upper leaf surface. I did say their eggs were yellow in my first comment :o)
we plant nasturtiums along side brassicas as a sacrificial/companion plant to encourage the cabbage whites onto the nasturtiums and not the cabbages.
the uk tent species are more orangey and have orange hairs, these do not.

OK