If it's the meter you were talking about before, the new price in the uk is about £190, vat on that is about £30, not sure about import duty but say £12, admin charge if it gets caught about £10 so a total of £52 or thereabouts. As long as the price your paying now is less than say £138 and the item is new then you'll still come out ahead.
I'm not sure of the limit on UK imports, so I'll take your word for it. I was surprised, though, since the Canada import limit is only $60! Taxes have to be paid for any gift declared over $60 = £30. What a gyp!
As for the original post, most of it's been answered: You are able to declare an item as a gift and not have the importer pay taxes, assuming it was declared under a certain limit (Steep is saying that £138 is the limit -- this can be looked up on the postal site). Anything over will be charged taxes -- well, not quite.
You see, it is very much dependent on the customs officer. Are they swamped with packages? What's his/her mood? Did they have a good breakfast that morning? Silly questions, sure, but that's how it works. Sometimes, items over the limit will only be charged a fraction of what it should or won't be charged at all.
Also (I'm not sure if this is how it works in the UK), but for transactions between US and Canada, how much duty (the cost of the customs labour) will depend on what courier you're using. USPS has always been the best, followed by Fedex and UPS.
UPS, in particular, has been well known to gouge out buyers in duty costs. It is VERY common for an unsuspecting buyer to buy a $100 item in the US, have it shipped via UPS, and almost pay the same price they did for the item in duties and taxes. See for example
here and
here.
I've done quite a few US/Canada transactions in my life and I tell ya, figuring out what you will pay is truly impossible. There are exceptions galore (for example, photography gear is apparently duty-free according to the North American Free Trade Agreement, but for that you need to apply for some sort of refund. Another example is that buying from Amazon.com (US) strangely does not require you to pay taxes and duties -- though I've no idea why not).
It's a given that a full fledged business will have special lawyers who know all the ins and outs. But the system screws over the Average Joe.
Last year, when I moved over to the UK, but forgot my expensive wrist watch in Canada, I wanted to have it shipped over. Keep in mind, this was a £2000 watch I paid for, including Canadian taxes. I realized there was no way I could ship my OWN watch to MYSELF without paying out of my ass. (That's not quite right. There's apparently a way, but it requires filling out a billion forms).