"What we are aware of and led to believe is that there are certain options being considered, one of which is an immigration centre or downgrading the prison to a lower category, " said Mr Hill.

BBC: Lincoln Prison gates

Three further Pyrenean tests loom, with Monday bringing a 187.5km stage with three lower-category climbs, then the hors-category Port de Bales, followed by a tight descent to Bagneres-de-Luchon.

BBC: Tour de France 2010: Riblon wins first Pyrenees stage

With AAA ratings still intact at two agencies and carrying a slightly lower rating from a third, Treasuries remained in the lower-risk category.

FORBES: Downgrade Follies