I think we're missing a bit of an elephant in the room when we talk about class representation, debating is very expensive.
To attend any tournament will cost you a not inconsiderable amount of money. Registration can cost from £10 to £50 per team, travel costs will vary with location but can be considerable, you also need your basic human requirements of food and beverages to sustain you. I would estimate the minimum cost per person per tournament is about £50 - but I haven't done rigorous math on it.
This is particularly an issue in debating compared to other activities as it is very difficult to practice it on your own, or participate at a distance, in the way one could with say competitive Chess. While societies do run their own training sessions that only get you so far, especially at less established universities, past learning the basics the only real way to improve is by competing against as many good teams as possible. So to get better at debating you have to attend as many tournaments as possible, which directly correlates with the amount of money you are able to spend.
While some debating societies cover some or all of the cost of attending tournaments not all are able to. This is particularly a problem at smaller or newer societies who don't have a history of donors, revenue or sponsorship. And even if one is lucky enough to have registration and travel costs entirely covered there's still costs of food, the near mandatory alcohol, and taking time off from any job you might have to support yourself at university.
In short you need to have a fair amount of money and time to spare to do this hobby, so it is unsurprising that those who do best at it are disproportionately well off compared to the general population.
Ideally societies with more money to spend could take this into account when hosting their tournaments and spend some on providing bursaries or reduced reg. I know some international tournaments have done this in the past, but by that point we are probably too late to deal with structural problems. More generally people should keep financial issues in mind when organising tournaments and try to keep costs to a minimum.
The above ignores financial burdens of going to university. I won't go into this in detail as there is a lot of good academic literature on the subject, but it seems pretty uncontroversial that the less well off are systematically less likely to attend university due to the costs of fees, accommodation etc.
Possibly debaters should look into inviting teams from colleges that do vocational qualifications, or contacting community groups. This is an area I know very little about so I'm hesitant about making any concrete suggestions, but I'd be very grateful for any comments.
This post was expanded from a comment in a facebook discussion and loosely follows up on my previous post A quick note on class in Debating. As a privately educated white middle class cisgender heterosexual man I am ridiculously privileged, so may have made mistakes that reflect that lack of understanding, please feel free to draw any to my attention. The note primarily reflects the UK Universities British Parliamentary Debating circuit, and is drawn from my anecdotal experience, so may not be universally applicable.