£23.99 in USD is currently $37.25. By comparison to the US, there are exactly ZERO blu ray movies, steelbook or not, selling for this price or higher, at any retailer, in any region. Even the highest priced exclusive steelbooks and digipacks here are much less.
The new G.I. Joe 3d 3 disc steelbook from Walmart is currently listed at $29.99 USD on their site, and people expect it to go on sale during release week. Les Miserables and Zero Dark Thirty were $29.99, but on sale for $22.99 and $19.99 and basically sold out at the sale prices.
Even the highest Disney and Pixar 3D 5 disc combo packs with lenticular slipcovers and all kinds of extras are $34.99 at a full retail (non sale) price. The only blu rays in all of America that might sell for more every now and then are from the Criterion Collection, but everyone knows those go on sale for $27.99 and $19.99 quite often.
So, I think it's appropriate to say that the newest prices from Zavvi are a little much, even by steelbook collectors' standards. Sorry just callin it like it is.