It is a relic of times past, when the English and French were both on the island. At that time, French pronunciation was not exactly as it is today. So, the tendency is a result of French influence, but it is a mixture of French (as it was spoken in England a long time ago) and English pronunciation as it has developed since then.
From which part of England do people pronounce the vowel “u” in a similar way to the French “u”?
It is a relic of times past, when the English and French were both on the island. At that time, French pronunciation was not exactly as it is today. So, the tendency is a result of French influence, but it is a mixture of French (as it was spoken in England a long time ago) and English pronunciation as it has developed since then.