Can anyone hazard a guess as to what this is

Rocket and Lambs Lettuce. I don’t know where the Lambs Tail came from.

If not salad it could be Nemophila, Baby Blue Eyes.

Rocket for sure..

I also think it's rocket. I've some growing at the moment.

Arugula is rocket I believe and it still looks like that to me.

It doesn't look like lettuce or rocket to me. It seems to be downy/hairy.
I think you are going to have to wait until it's a bit bigger before you can identify it.

I use an app called, Picture This. Focus on any leaf and it will identify any plant/shrub/tree followed by detailed advice on whatever leaf is identified.

Could it be rocket and lambs tail HurdyGurdy?

There are apps called WhatPlant or Plantsnap. I think they are free but not sure. You take a photo and the app identifies the plant. Pretty accurate in my experience.

Many of the leaves look like Arugula but maybe a bit rounded. Not always easy to tell from a photo but that's what it looks like to me.

Did you plant any cinneraria? The kind with silvery leaves? They look a bit like this when the come up first.

Did you have any seeds of any of the more alternative salad leaves - lambs lettuce, for example?

Thank you - it could actually be lettuce. Definitely not rocket, as I didn't have any rocket seeds, but I did have lettuce seeds.

Will investigate further - thank you

Looks like Rocket, I would taste a tiny piece.

Could it be lettuce.