Veganuary 'action' team photo op

The vegan advocacy organisation 'Veganuary' is seeking a photographer on Monday 15th May in central London. We are looking to capture group photographs of our team (approx 35 people).
The sole objective is to capture dynamic, vibrant photos for use on our website, social media, brochures etc.
Our concept is to stage an action / demonstration in Trafalgar Square (though there is no real purpose behind the action / demo other than to capture the photos!).
I have attached some examples. Someone with experience of taking similar photos preferred.
We are allotting between 1 and 2 hours for the photo shoot.
I am in the process of seeking the necessary permissions to use Trafalgar Square.
Flexible budget. Open to discussion.
Visit veganuary.com to learn more about the organisation.