I think it's a fair point that if a Tory had said this there would have been a twitter frenzy of epic proportions and he would have had to issue a grovelling "clarification" in order to keep his job.
HOWEVER, I don't think this is all down to some left wing hypocritical conspiracy, it's to do with certain statements fitting into a narrative and an expectation that the parties have basic tenets which mean that an apparent action against that tenet is seen as less threatening than an identical action from the party which would normally be expected to hold those views.
Ok, I'm explaining this appallingly, I'll try to give a hypothetical example.
Labour MP makes statement which appears to suggest certain NHS services may need to be privatised. MP told to pipe down by Miliband but overall not much fuss.
Almost identical statement made by Tory MP, mahoooosive fuss, MP withdraws comments in order to avoid having whip withdrawn.
This is because people trust Labour to, at a basic level, support the principle of the NHS. Rightly or wrongly, they do not trust the Tories on the NHS so those comments would play to that narrative. It's the same reason why Labour is generally in a better position to reform public services as the public generally thinks it is on the side of the NHS etc. Reverse this and many polls have been done which show the Tories are better placed to make cuts in the armed forces because people feel, rightly or wrongly, that they believe in a strong defence. So it's a case of "well they wouldn't do anything too bad, would they?"
So back to Lammy. The reason why he hasn't been castigated like a Tory would have been is because, at a fundamental level, people think that he cares about the people who live in Tottenham and, even if they disagree with what he has said, generally don't think that he has said it from a negative standpoint. However, if a Tory said this, it would confirm the nasty-party perspective, people would assume that he had no understanding of the people he was referring to and was being classist and also probably borderline racist and hence it would be a whole bigger story.
I did my politics degree a long time ago :(
Anyone able to explain what I'm trying to say a bit better??