With thanks to the Media Office of the Archbishop's Council for this background detail to TV licences and related matters to showing the Royal Wedding on 29 April 2011:
What licence you need
Whatever the context you need a licence to watch or show any TV broadcast live (or almost live). The TV licence is attached to a building. Usually that means a house. But there's no problem showing a programme in a church building or a hall as long as you have a license for that building - the licence for the vicarage next door won't do.
The size of the audience is irrelevant. Some churches got a licence in order to show World Cup matches on a big screen. From the TV licensing point of view there's no problem showing the wedding to a large group in church as long as you have a licence for that building. It makes no difference whether you are showing it on a TV or through a computer, or whether you are projecting it.
It is considered almost impossible for a church to show the wedding in the open air without a special licence from the broadcaster, which is practically impossible.
A lot of people think that charging for admission makes a difference. In fact it doesn't make any difference to the need for a TV licence. There's nothing in principle to prevent a church from charging. The tricky bit there is that if you sell tickets for an event it may start to look like a show rather than a party or a community event - and that might mean you would need a public entertainment license. It would be simpler to ask for donations, as you might for a Summer Fair.
Public entertainment licences
These are provided by the local authority. This is normally needed if you are going to gather an audience for music, dancing, showing a film etc. But there are specific exceptions for acts of worship and also, crucially, for watching live TV broadcasts. So there shouldn't be any need for a public entertainment license on that score.
A public entertainment licence would be needed if a church wanted to sell or serve alcohol. A church would also need a public entertainment licence if the event were to include music (live or recorded) or dancing. (Worship is excepted.) A licence is also needed to show a pre-recorded TV programme or film (unless the context could be described as "training")…so you couldn't record the wedding and show it later.
As long as the building has a TV licence for the building (which costs £145.50) a church can have a party including food, dancing, worship and most other things.