Azure's EU servers are in Dublin (North Europe) and Amsterdam (West Europe). As for your rankings, it should not make a difference whether you host your site in Ireland or the UK, I just wouldn't recommend hosting it in the US if your audience is mostly from the UK. Latency-wise, UK-based hosting would still be your best bet, but the difference with Ireland is tiny. I'm sure Google understands that sometimes it's better, easier or cheaper to host in a neighboring country.
If the UK if your target audience, try to make sure you have plenty of other signals that point this out.