David Cameron's Conservative Party has failed to throw off the label of being the "nasty party", has shown itself to be "racist" and will do or say anything to bolster its poll ratings, according to a leading black Tory adviser and former Thatcher speechwriter, Derek Laud.

Writing exclusively for The Independent on Sunday, Mr Laud says the Prime Minister's controversial election strategist, Lynton Crosby, had effectively signalled last week that the next general campaign was under way and would feature dog-whistle tactics on race and immigration like the "same old Tories".

Mr Laud writes that he is saddened that Theresa May's bravery of a decade ago, when she publicly admitted the Tories had become the "nasty party" and were in danger being unelectable, has been ditched.

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He complains the Tory leader's "modernity agenda" has run "into the sand" and that the recent rise of immigration issues is no coincidence. Mr Laud's attack follows immigration spot checks at railway stations across England last week backed by the immigration minister, Mark Harper. The Equality and Human Rights Commission is to examine the powers and justification of the checks.

His article, less than two months from the Tory conference, is likely to inflame the debate about what the party needs to do and say to win outright in 2015.