Portugal, UK, Ireland have been in UTC for ages.
GMT as a time standard is defunct. The Mean Sun no longer traverses his notional sky.
GMT as a civil time zone is based on atomic measures[0]. It is not measured from the meridian. This is the phrase used to indicate this in UK legislation:
In these Regulations Co-ordinated Universal Time (UTC) is the same time as Greenwich Mean Time (GMT)
[0] Time scale UTC(NPL)