Those are not Cucumber Beetles, even though they are on Cucurbit plants. It can be tough to identify a small black beetle even when a good clear picture is provided and yours might be innocuous or beneficial, but probably not a pest.
Flora may have an answer or some place in the UK you can go for identification.

Asad, they are what you would refer to as pollen beetles. They feed on the pollen of flowers, not really causing any damage as they do so.