Where there is habitat and food..wild life will follow..
But to be successful you have to start from the bottom of the food chain.
Encourage lot of different insect by providing some little pockets of 'wilderness' here and there. If every allotment would have square metre of nectar plants..that would already make big difference.
But it doesn't have to be just 'boring' flowers..leaving odd onion/leek to flower..or cauli...maybe some sown under a apple trees where proper crops are difficult. Mulching provide hiding places for lot of things.
You just have to be 'untidy' in tidy way..tidy enough so nowbody complain that your lottie is in mess.
If there is hedges..don't rush to trim them too early when birds are nesting..or..if there is parts flowering..let them finish first and then trim.
It is not big effort..just thinking what is beneficial and leave it be for bit later...let nature reap benefits from its crops. There is too many gardeners still around who keep their plots and garden immaculate..tidying every fallen leaf and twig away..and those 'spray bottles' are still used to kill for what ever may or may not be threat to their plants. Less that and allowing some creepy crawler's to be makes garden grow much better plants.. ;) Once you plot is rich with insects..you get more and more their predators coming...and then birds..and if birds have somewhere to nest, they will stay,,,and then comes bigger birds,,,etc,,,and the last and final is big ugly 'committee' bird that will 'sing' "you've gone too far now"... ;D ;D