Clearly these are some type of Pieridae/cabbage butterfly caterpillars. The adults/butterflies are predominantly white, often called 'whites', but not being familiar with UK butterflies, I'm not sure which one. The yellow butterfly may be in that category also, some of the 'whites' having yellow or orange on their wings.

Here's a link to members of that family in the UK.

Sherry

Here is a link that might be useful: UK Pieridae Butterflies and their Larvae

My immediate thought is Cabbage White or something in the Pieridae (Whites and Sulfurs) family, although Pierids don't usually stray outside the Brassica Family (Brassicaceae) as host plants. Another possibility is that these white butterflies are actually day flying moths.
Where in the UK are you located?

John

I'm in Southwest UK (Wiltshire)

my first search online suggested it was a cabbage white. but thew adults land with wings closed so couldn't see the markings,

the day moth I always thought moth was a night!

I have also spoted them on my kale and purple sprouting broccoli

thank you

Leo

Lucky you on those caterpillars. I love those white moths. Been dying to get some host plants for the white moths I see!

well, o haven't got on top, it's made my Brassics holey like a colander! :'(

but I don't hate butter flies id love to keep some but they need so very much room? :)

A beautiful caterpillar photo.