The general designs and function of a church or place of worship makes general security more complicated but a great deal can be done at a modest expense:

Locking your church at all times unless a responsible person is present.
Small valuable items should be stored away in a locked vestry, cupboard or safe when not in use during the week.
Altarware – wooden or base metal substitutes should be displayed and the originals locked away. They can be returned for services and events.
Antique furniture and other valuables – consideration should be given to discreet chaining to floor and wall. This may not deter the determined thief but may be sufficient to prevent the opportunist criminal.
Valuables should be kept in a safe or a strong room when not being used for a service.
Valuables, including communion plates, which are not in regular use should be deposited in the bank.
Keys should be kept by a responsible person or in a secure place away from the church.
The vestry should be secured by good quality locks and bars at the windows. All locks should conform to BS 3621, or higher, specification.
All property should be photographed and a log kept. This needs to be stored in a safe place away from the church. It’s a good idea to use a coin, such as a 50p, to indicate size.
The offertory box should ideally be emptied daily. A notice should be displayed on the box indicating this.
Vulnerable stained glass windows can be protected externally by polycarbonate sheet.
Be vigilant and report anything suspicious to the police at the time.