Many sellers registered in China have fulfillment centres based in the UK, and so will often send the items from within the UK. However, some Chinese sellers post items directly to the UK from China, so if this is what your seller is doing then there is a possibility that your item may either still be en route to the UK, or it has arrived in the country but has been held up in Customs.
In the event that your item has been held up in Customs you will more than likely hear about it sooner or later, as you may well be required to pay import charges on the item before it is released. However, this is not always the case, as some items arriving from overseas have been known to slip the net in the past.