When we're away from home, we try to worship at a church nearby. One thing I notice is that the more successful a church is, the less friendly the congregation. We went to a wonderful choral Eucharist this morning in London. Everything was perfect and the church community was obviously doing all the right things except...when we went and had coffee in the hall nobody spoke to us. You know when you're standing there, you catch someone's eye, and their gaze slides off you and they're off to find someone more interesting? This happened several times and was so dispiriting, especially as everybody around us was engaged in back slapping, hugging and animated conversation. After a while we gave up and left. It wasn't the end of the world for us, as we were only visiting, but I feel sorry for newcomers to churches that behave in such a cold way to newcomers.
In my experience friendliness at churches is mostly fake and designed to sucker you in. Once they have got you they will turn on you. If you were only visiting there was no need for them to bother with you as there was no possibility of you becoming a regular attendee at their church.
As a side note London is a huge city and I wouldn't expect people to be as friendly as a small community in or out of a church setting.
My experience as a church visitor is mixed. Asa general rule the larger churches and busier churches are more likely to,have welcome teams but they are also more likely to,ignore you as everyone is trying to,catch up with someone about something at coffee time and ignore the visitors. As most of my church visiting is done when I'm checking out a church prior to applying for a job I know that, even when they know that stray new folk may be a priest in disguise, they still ignore you. I didn't apply to,the one where as our cover was blown they assumed my husband was the priest. Err no.
My experience is that the smaller and medium sized churches can be very welcoming as new people are more obvious. We had three in yesterday and the congregation were chatting away to them at coffee and I managed to catch a brief word with all the new people. We may not be the sort of church they are looking for, we are on the edge of a city so there is lots of choice, but for welcome (and cake) we are brilliant.