I don't think that being a cousin is a protected class. You can consult an attorney of course but it appears that you are referring to an 'arms length' exclusion. The sale is supposed to occur without any influence of family, etc., I've seen listings where the seller has the listing put right in the listing 'uncle joe smith is excluded from being able to purchase the home' etc.,
A 'non arms length sale' occurs when the buyer has influence over the sale. Sorry that the house you want may not be available to you. A lot of these situations happen because, at the end of the day, the people involved with the sale and the banks do not want any scent of an unfair arrangement.
Haven't been in UG for years, grew up in Bristol....
Regardless of your intention, some might be attempting to purchase the home to help out the cousin and to sell it back to him when he gets out of jail. There have been many cases of friends or family members doing this and continuing to allow the previous owner to rent the home back or even just to live there - for less than when they owned the place. These are the things fraud is made of. So, in general, I support the policy.
If your intentions are pure, consider writing a letter to the bank explaining your relationship - whatever it is -and your reasons for wanting to purchase THIS home. Who knows? Maybe they will approve it. But, I urge you to be honest and forthcoming.