People may be interested in the following extract from a BTO newsletter.
Given fair weather, late broods could still make it to Africa
It's not been easy for Swallows this year. Many returned to the UK later than normal this spring, having been held up by poor weather further south. However, it appears that some may be setting off late this autumn too. This year we have received reports of at least seven nests still containing young in October, with one brood fledging as late as 11 October. This is quite unusual - of the 45,000 Swallow nest records collected by the BTO Nest Record Scheme since 1939, only 16 Swallow nests have ever been recorded with chicks in October. Have you had late Swallow broods? If so, let us know by emailing nrs@bto.org.
Further info at the following link.
Ian Harrison