To answer the question I would have to say wear what you feel comfortable in! Virtually anything you like as long as it is respectful. The important thing is that you come along. You will be made welcome whatever you wear!
Gone are the days when only the “Sunday Best” was good enough, although you will tend to find that older members of the congregation tend to do what we would call today “Power Dressing”, old habits die hard. You will find many men just wearing “Smart Casual”; sports jackets and slacks; open neck or polo shirts; or jumpers and pullovers. The ladies tend to out shine the gentlemen – but don’t they always!