This is caused by your skin overproducing melanin (the chemical in your body that makes your skin tan)
SPF is a very strong guard against aggravating this problem, make sure you buy a good quality face moisturizer with at least spf 20 and use it even in the winter sun. Brightening products will usually help with this, there are lots of essential oils and other ingredients in these products that will reduce pigmentation and slow down the production of melanin if you don’t want to go with invasive treatments and peels.
This website is a very good source of information for you on this subject and gives some good suggestions of products you can buy.http://www.dermacaredirect.co.uk
Try to find something that helps keep this condition under control for you on a daily basis rather then going for treatments. A good massage treatment will also help as a back up,as it increases the circulation, if you can go for prescription facials, but if you can’t, look up some good massage techniques online and do it yourself