Well... they are both in the same family. However, while researching I read:
'Where to see them
Swallows are found in areas where there is a ready and accessible supply of small insects. They are particularly fond of open pasture with access to water and quiet farm buildings. Large reedbeds in late summer and early autumn can be good places to look for pre-migration roosts.
When to see them
March to October.'
This information made up my mind. They are........Swallows!I realised this by the quote 'are found in areas where there is a ready and accessible supply of small insects.' This was because while watching them I saw hundreds of thousands of little insects swarming around the sky. And this is why the swallows were here! Hiding in the tree did prove successful because they came very close to me so I could get a very good view!