3 hours ago Steven McIntosh Entertainment reporter Sir David Attenborough says thank you for birthday messages Sir David Attenborough has said he has been "completely overwhelmed" by the messages he has received ahead of his 100th birthday. The veteran broadcaster and environmentalist celebrates the milestone on Friday, with a special concert planned in the evening at the Royal Albert Hall in London. In an audio message released on Thursday, Sir David said: "I had rather thought that I would celebrate my 100th birthday quietly, but it seems that many of you have had other ideas.…