I don't think the “or the chair” option is on the standard form as issued by Fair Trading nor should it be (although it's not illegal). I simply encourages 'blind' voting which is generally a bad thing.
To get back to Muffin's point. You can't assume that a proxy given to one person can then be transferred to another proxy – unless perhaps you had “or their proxy” on the form as Peter C describes.
In any case, you don't have that so it's a question of getting the original proxies reissued in the name of the person who will actually be at the meeting. It sounds like it's going to be quite controversial meeting so all this paperwork has to be watertight and a proxy of a proxy certainly isn't that.
New proxy forms properly signed and dated supersede any previous proxies issued.