Justin Urquhart Stewart, our favourite London investment manager, tells a joke about the eurozone members in a school room. The Irish and the Greeks are the slightly unruly pupils in the middle rows, launching paper aeroplanes at the studious boys, the Germans, seated at the front. But, he says, don't let the British boys join: put them into the euro class and they'll be lobbing empty lager cans from the back seats.

The self-deprecating national joke comes to mind in the week that ratings agency S&P put Britain on credit watch, warning that it may be stripped of its AAA rating.

The Daily Telegraph reported the news as follows: "Britain's economic stability has come under the gravest scrutiny yet again after the government's debt was placed under official review by the world's leading ratings agency for the first time in more than three decades sending shivers through the currency, gilt (bonds) and stock markets" because British debt may be heading up toward the long-indebted levels of the Italians at over 100% of GDP.

The news appears to have helped push the interest rate on the 10-year British bond up by a significant 17 basis points (0.17%) in the week to 3.7%. Any move is significant because the British are of course supporting the capital value of their bond debt paper by purchasing their own bonds.

Ireland appears also to have suffered slightly from the British fallout, with the benchmark 10-year bond here rising by nine basis points to 5.25%.