Generally speaking, many in England find nationalistic flag-waving distasteful (with the exception of England playing in a major sporting event, or, for some, when there's a royal event).

In the last few weeks, far-right groups have tried to push the narrative within their circles that "we are 'not allowed' to fly the flag and 'be proud of our country'" (dog whistle for ethnic nationalism and anti-immigration + anti-asylum viewpoints). This led to people putting up flags on lampposts, spray-painting it on pedestrian crossings and bus stops etc. Councils initially started taking them down off lampposts, but then the far-right people were able to say: "look, it's proof that we're not allowed to fly our flag" (aka "the 'true Brits' are being suppressed by the 'others'") so councils have largely backed off.

I think it is essentially used as a dog whistle to make "others" feel unsafe. Certainly that is how I feel when surrounded by these flags.

That is not to say that everyone is putting them up for these reasons, but if you are putting them up now, I think it is a way of showing a particular point of view.