The bank indicated it would defend this level unless oil prices fell to $30 a barrel. With Urals blend still around $43, the rouble's value currently looks in the right ballpark. The trouble is that currencies tend to overshoot as they decline. Forward markets are pricing the rouble 18 per cent lower against the dollar in 12 months. And the bank cannot afford indefinitely to keep burning through its remaining $386bn foreign exchange reserves, which have fallen since August by nearly $10bn a week. The pressure on its reserves was highlighted by Fitch's downgrade on Wednesday of Russian foreign and local currency ratings to two notches above junk, in line with a similar move by Standard & Poor's in December.