I don't think anyone was denying that the British did a good job trying to close down the trade. That's something to be grateful for - but it doesnm't wipe out the centuries of slave trading and slave driving tat preceded and helped motivate it. Hence Tony Blair's statement.

John Newton got it right:

Amazing grace! How sweet the sound
That saved a wretch like me!
I once was lost, but now am found;
Was blind, but now I see.