Customs are VERY slow at the moment. I waited for over a month for a frame from US sent early December.
Is it being sent via USPS? if so you may be able to find out where it is at your Parcelforce depot, dependent on whether the bloke on the counter is a helpful soul or a jobsworth...
P force will have a list of every package entering the country by post code, and the town of origin.
Fr'instance; my frame was sent from Boise, ID. Unsurprisingly, It was the only parcel sent from there to my postcode. From that, the extremely helpful chap at parcelforce found both the US and UK tracking numbers, and plugging them in online, I found where it was.
It really does depend on the counter staff though. His colleague was extremely unhelpful and denied that anything was possible without a tracking number.
If it's gone via a different service I would imagine something similar is possible, but if it's coming from a major city there may be too many numbers to trawl through...
Give a man a gun, and he can rob a bank.
Give a man a bank, and he can rob everybody.