Next October I going to the US from the UK. I want to buy a Macbook Pro as it's much cheaper over there. I was going to take it out of it original packaging and put it in a laptop holder. My question is, can they confiscate it?
I question your premise. Take the 15" Macbook pro with retina display.
Price in U.K. is GBP 1332.00 + 267 VAT = USD 2035.00 + VAT (using exchange rate today)
Price in U.S. is USD 1999.00 + State sales tax.
So the difference in pre-tax price is less than 2%. The apparent price difference is mostly your country's tax.
If you buy it at retail, say in New York state, you might pay 8.25% sales tax and your credit card will probably eat another 2.5% on top of the interbank rate for currency exchange fees, so your 1999.00 USD purchase costs you 1448 GBP. The state sales tax is not refundable to visitors, by the way.
So your net savings, assuming you get away with smuggling, would be 181 GBP, or about 11%. You may also need to buy the Apple World Travel adapter kit @25GBP or 29 USD if you don't want to carry a plug adapter around forever (the power adapter itself will work fine on UK voltage, but the plug is wrong). If you pay VAT at the border @20% you'd be in the hole by about 100 quid.
While laptops and jewellery may seem easy to smuggle, people get caught every day. Even a cursory look by a suspicious customs agent will probably reveal the deception immediately.
Yes, Commissioners of HMRC have broad and ancient powers to seize goods they suspect are illegally imported.
In this case, unless you can satisfy HMRC that you were not importing the item, you will have to pay a fine and the appropriate duty and VAT on the item. I am not sure I agree with Relaxed's post, I think in this circumstance the item might be detained until you have paid the bills.
On entry, you are legally required to use the Red Channel ("Goods to declare") and report the item to an HMRC officer. (At domestic baggage claims there is a red telephone to use instead.)
In reality, if you decide to ignore your duty to report it, I think it is quite unlikely that you will be caught. I have passed through a UK Border with my MacBook probably hundreds of times and no one has ever wanted to look at it.
Adding an answer from personal experience...
I purchased a laptop on a trip to California in 2012. When I returned to the UK, I went through the 'red path' and showed it to the inspector along with about GBP 400 of other stuff I had purchased. The other stuff was generic, like clothes and some USB sticks and what-not.
The inspector typed something into her computer (don't know what), and said that I was over the limit and the duty on my stuff was about GBP 410 plus VAT. And since the laptop was a single item over the limit, it needed the entire duty paid. Then she thanked me for declaring my stuff and went on to the next person. No duty, no VAT, no confiscation, no nothing. Just a 'thank you'.
So I packed my stuff back into its bags and went on out. That was at Heathrow.
Another time I came back from the continent and I was over the limit on 'fortified wine'. I went through the 'red path' to declare it and nobody was there, this was about about 9 PM at Manchester. I waited around until it became obvious that nobody would show up, then I started calling HMRC.
After a few calls I was able to speak to someone and they said they would send an officer from Liverpool to inspect my 'fortified wine'. After about an hour, the officer arrived and collected the duty, it was about GBP 20. I also used their complaint procedure to record that the waiting time was unsatisfactory.
These are only personal experiences and they seem out-of-whack with HMRC's published material on their web site. I think it's good to know that sometimes they let you off the hook for reasons known only to them (it might be an appreciation of your candour) and sometimes the 'red path' is not staffed leaving you with a decision of conscience.
If you opt to go through the 'green path' you are subject to a random selection where your demographics and where you arrived from may play a part. If you are selected and get caught they will probably not let you off the hook because you would be in a position to be aware of what the 'green path' means. I doubt very much that they would confiscate your laptop, instead they would give you an invoice for the amount due and send you on your way. And they would turn the invoice over to their chasers.
While they might detain it until you have paid all applicable duties and taxes, customs officers are not primarily interested in seizing goods that can be imported legally. That's what happens to illegal drugs, weapons, some foodstuff or counterfeit goods. For a laptop, if found out, you would be slammed with a significant tax bill (mostly VAT, some duty as well) and possibly a fine on top of that.
It could even happen years later, every time you cross the border (or theoretically even elsewhere, although that's even less likely), they don't need to catch you in the act the first time you cross the border with it.
Note that travelling by air from the US to the UK, you have a GBP 390 allowance and rather favourable rules for goods under GBP 630, so it should be possible to import a cheap laptop completely legally with not much duty or formalities, but a Macbook Pro will have to be declared to customs.
The chances of you being asked about a laptop is near to zero. I have travelled in and out of the US hundreds of times with two laptops, an iPad, two iPhones, iPod, headphones, disk drives, digital cameras... the only thing they have ever looked at was the drives looking for kiddy / animal / snuff porn.
I've brought almost brand new electronics from my work, in and out of the country on a regular basis - I had no problem, mainly because its not illegal.
That said, legally you should declare all items over your allowance.