Two suggestions... use a bottled saline solution (no other ingredients) to irrigate the sinuses ... at least 4 times a day. During the colder months with dry heatedair, the sinuses can become inflamed and produce greater than normal amounts of mucous. This is the likely source of your sore throat. Look at your throat in a mirror and you'll likely see some red streaking going down the back of the throat, which is the results of the infection from the sinuses draining down the throat.
Secondly, a product here in the U.S. called 'Smart Mouth' is a zinc based mouth rinse that one uses once or twice daily. (Seen here:
http://guessingallthe...t-anymore-smartmouth/ ) We've used it for over a year and the results are unbelievable...one of the few things in modern life that does what it says it will do. Nice thing is that for travel (which I do constantly) it comes in small pre-mix packets that one just tears the top off and both ingredients are emptied from that. Highly recommended... I would assume this product or one like it is available in the U.K.
One last suggestion... use a Water Pik instead of flossing.... much more effective... there are several brands available...