Since the correspondent chooses to remain anonymous it is difficult to provide locality based advice.

As to the general questions:

The situation shown in the image does from time to time occur,; but the people identified as "contractors" are within LBEnfield either direct employees or agency staff 

The extent of the obstruction depends on the particular housing estate in which the highway (footway) occurs since (for example) roads on the Deansway estate within the pre-1965  Edmonton Borough Council envelope are materially narrower than those west of the A10

I do suggest that

• T Gilbert makes representations to their Ward Councillors (three per ward);
• endeavours to appear at the relevant Ward Forum and raise it as an issue
• raise a formal written complaint