BBC Radio Solent tweeted a picture of a road closure (apparently near Winchester):
In the background, there is a road sign with two red lights on and a yellow “symbol”. What does it mean?
Looks like a “Temporary lane closure”.
The situation in Winchester, you referred to, supports this.
See another example from gov.uk
Temporary lane closure (the number and position of arrows and red bars may be varied according to lanes open and closed)