So the answer is...it depends.

It comes down to the question of domicile, which is quite a complicated area. Generally speaking, UK domicile is determined by where you're born and where your father's born. But you can also be ‘deemed domicile’. In other words, under the current rules, if you've been living in the UK for 15 out of last 20 years, you would then be classified as ‘deemed domicile’ and therefore, inheritance tax would be applicable on your worldwide assets. Now, if you're born and resident in the UK, and you're just ordinarily domiciled here, then effectively all your worldwide assets are liable for UK inheritance tax.
For those who want to lose or stop their UK domicile, they have to be abroad for at least 6 years and make sure that they don't keep any access to any anything in the UK at all. To the level of making sure your Will says you're not even buried here in the UK. (So, no bank accounts, no assets, absolutely nothing.) After six years of this situation, you can change your domicile and therefore you won't be liable to tax on assets abroad.

Generally speaking, worldwide assets are liable to UK inheritance tax if you are UK domiciled or deemed domicile.

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