Chief Secretary to the Treasury Danny Alexander said the £25 billion investment from insurance companies into British infrastructure projects was a "massive vote of confidence".
Speaking at the construction site of National Grid's London Power Tunnels, Mr Alexander said the investment was "more evidence we are rebuilding Britain."
More top news
Some 66 people have been killed after the plane they were travelling on crashed in southern Iran.
The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.