Can anyone explain why my 65 plate polo has just this winter started having really thick condensation inside the windscreen, so much so that I have to use a windier cleaners squeegee whenever I want to go anywhere. Plus that fact it’s been freezing inside this past week?

Seems to be very cold and damp this winter, both inside cars and also houses.
Warm inside, cold outside with little ventilation is the cause of condensation.

You can use silica crystals or salt in a pot to draw down the moisture and Halfords sell a condensation bag (full of silica crystals) which works really well
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=halfords+condensation+bag&_sacat=131090&LH_TitleDesc=0&_odkw=karcher+window+vacuum&_osacat=131090

Otherwise it is a case of drying the interior or using an electric squeegy (Karcher do a great one) https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2499334.m570.l1311&_nkw=karcher+window+vacuum&_sacat=131090