As HMG's page on the subject says:
Your duty-free allowance means you can bring in a certain amount of goods for your own use from outside the European Union (EU) without paying duty or tax. When you’re bringing in goods you must:
transport them yourself
use them yourself or give them away as a gift
So these are the rules that cover bringing in gifts for UK residents. After discussing alcohol and tobacco allowances, it goes on to say that
You can bring in other goods worth up to £390 [...]
If a single item’s worth more than your allowance you pay any duty or tax on its full value, not just the value above the allowance.
It goes on to note that you must
Declare any goods over your allowance. Your goods could be seized if you do not declare them
You don't say what this "Razer Blade" is worth, but if it's more than £390 you should declare it, preferably with documentation as to the purchase value, and be prepared to pay duty on it.