A BBC blogger is raising the possibility, after noting a couple other names:

If not Chris Patten or Ann Widdecombe, then perhaps Paul Murphy, the former Secretary of State for Northern Ireland — a devout Catholic and a papal knight — will be approached. And if they wish to stick with a Northern Irish theme, they might even consider Ruth Kelly, who also served in two Labour cabinets and is said to be a member of Opus Dei. As with all high-profile candidates, there is the question of remuneration, and some former MPs, like Ann Widdecombe, are earning significantly more from their business and other activities than this position is likely to pay (roughly £100K, I’m told).

Which brings me to a possible candidate who doesn’t appear to have been sounded out yet, who could easily afford the pay cut, and is not only a high-profile Catholic politician, but a recent convert. In fact, Francis Campbell once served as his private secretary in Downing Street, and his efforts were eventually rewarded with the most talked-about ambassadorship of the moment. How about His Excellency Tony Blair, Her Majesty’s Ambassador to the Holy See? It has a certain ring to it, don’t you think?

There’s more, of course, at the link.