How many services are there?
As of 2020 there are 96 services open and signed from motorways in Great Britain. That's counting dual-sided services as one (including Stafford and Sedgemoor), including three places classed as rest areas, but excluding truckstops signed with black signs and excluding Appleby Magna petrol station. By 2021 two more are expected to open.
Northern Ireland has a further 3.
We reckon there are 216 more service stations officially signposted from A-roads in Great Britain, but this is harder to measure as the quality of signage is very inconsistent, some of them operate in pairs and not all of them are on major roads.
There are 6 more official motorway services in Ireland (Republic Of.), and 10 more semi-unofficial ones.