It is certainly possible with these type of forums but, as LeeK, mentioned above this will eat away at the sites bandwidth and webspace.
The best alternative would be for UKDirt to create a YouTube account and host all videos there, away from it's own webspace, thus saving on bandwidth and not compromising on server load times.
By hosting the videos on YouTube, UKDirt could also take advantage of the possible cross-site traffic, meaning YouTube users that 'stumble' across the videos simply by typing 'Banger Racing' or F1 Stock Cars' in the YouTube search box may not know what UKDirt is and visit the site to find out, meaning possible new signups direct from this source.