We have no official religious figurehead or authority in the UK. The govt is secular therefore does not dictate on religious matters. What has happened over the years is that we have developed some plurality around the issue of moonsighting.
Traditionally as you know an Islamic month ends on 30 days, or the 29th day if the moon is sighted - historically this has always been done by telescopes. Since Sallelites came about we are able to tell exactly when the new moon begins using technology.
The question then arises - do you continue to sight the moon physically or do you rely on the scientific data? That is one arguement.
Another arguement is that in modern times, we can communicate information across the globe in a matter of seconds. It used to be the case in the past that different communities could have had eid on different days based on their ability to communicate moonsightings. Today we can communicate within seconds - so should we celebrate Eid based on a global moon sighting or a local one?
This gets even messier, in the UK we often have cloud, so it is not possible to sight the moon, however you could sight it in the South of France or North Morocco for example. There is an opinion that this distance should be considered "local" to us. Then this is extended to people in the same time zone, so some UK masjids have accepted moon sightings in South Africa (which we share a timezone with) but not with Saudi Arabia, who are several hours ahead of us.
To complicate matters further, there is scientific data available on whether it should be possible to sight the moon or not. There have been arguements on the validity of sightings based on the possibility of seeing the moon.
This is why we have moonsighting wars, this stupid kitchri of ego.
For some reason the British govt has kindly provided guidance on whether it should be possible to sight the moon or not. I suspect it's probably because they want to limit the potential economic impact of Muslims taking off Eid on short notice. I've always booked off both days just in case, but people who are self employed can just stop when they like.
@Imran Khan read this please to understand UK govt position.
