A peak under a leaf

Graphosoma lineatum according to google image search, some type of shield bug.

If that's in the UK, they might be soldier beetles of some kind, but hard to tell from the side and/or closer.

In passing, as a first approximation, (true) bugs suck, while beetles chew and have hard wing cases (which is what these look like having). But there's plenty of examples to the contrary!

Shield bugs have a wide often colourful "shield" as their back - it's hard to believe you wouldn't have noticed!