Kitchen tap

I have a new kitchen tap, with different pipe fittings. I am a complete amateur so please bare with me.
I have seen taps supplied with 4mm copper tails that can be joined into my existing pipework.
Are there standard pipe sizes in the UK? I have been looking at some tasty european taps that are supplied with 4mm hoses with 19-20mm connectors to connect into the pipework, but the existing connectors under my sink are bigger. Can I use Europen fittings or should I figure something else out? What do you recommend?
Thanks.
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