I fretted over this one quite a bit, partly on here as well. I did some volunteering at a local church - food bank and homeless shelter are linked. I always just assumed it was "wrong" for me to attend a church as a non believer, but the activities happened to take place there.
Then a few odd things happened in my life, including that the 4 friends I had in walking distance moved away. They managed to time this just before my dad got sick and died!
I do know my neighbours but it felt like a sudden loss of support and I'm in London so other friends dotted around everywhere, and I hate having to travel an hour to socialise already.
so one day I told the vicar's wife what I was going through with dad's illness and she wanted to help. I explained I didn't believe and she said "so what, this is about community". And I thought, given I don't have my local friends any more, I could do with more community support.
I've attended services after that because of the "community" factor and when it came to communion, explained to the vicar's wife that I'd hang back. She said "well, we pass it round, so you'd have to refuse it, which is fine, but we're happy for you to share". I said "huh?" and she said "well I think the point is to share with everybody".
I'm sure many MNers will be horrified by this though. Don't know what other churches do as I've not been to any others.
I'm not sure what I'd put on the next census.