He's referring to the current animosity between the UK and Europe. Both groups frequently go out of their way to make life harder for the other. The EU proposing the English GMT would be unlikely in this climate. Also FWIW I think only Portugal overlaps with GMT.
English is an official EU language is one of the (few) working languages of the European Commission (French is also used a lot). And the United Kingdom remains a member of the European Space Agency. GMT overlaps with European time zones, with countries like France being big proponents things like UTC (and TAI, and the metric system in general).