The treatment of a generation of British citizens who live here, work here and vote here has been truly appalling. Theresa May, who as home secretary created the environment that allowed it to happen, should never be allowed to forget it.

But the problem with May starts with David Cameron. As prime minister, he failed to stand up to her and allowed her to reign supreme over Home Office matters, knowing perfectly well she has always had suspect judgment. For example, as home secretary she insisted that international students should be counted in the official immigration figures, and made it more and more difficult for them to obtain visas to come and study for the first-class education for which Britain is world-renowned. The elite universities protested, but May doesn’t do listening.

As if that were not daft enough, May introduced the “Go Home” vans, targeted at illegal migrants. I was not alone in strongly criticising this initiative at the time, and the policy was later dropped.

Now we all know that in 2012 May was allowed by Cameron to create what she herself called “a hostile environment” for illegal migrants. But even I could feel her hostility.

I am the son of Jamaican parents, who are part of that Windrush generation. They came to the UK in the late 1950s, and were soon, through their own hard work, members of the property-owning democracy. I vividly recall a conversation with my mother about her reasons for leaving Jamaica. She explained that they responded to a request from Britain, which needed citizens of the empire to assist in the urgent task of rebuilding a country destroyed by conflict.

Families like my own came highly skilled and many more were well-qualified professionals. Without them we would not, for example, have the National Health Service we have today.

I could not be more proud of my mother’s explanation, even if she, many years later, was less impressed by some of my own. The first such difficulty came when I had to explain why I had joined the Young Conservatives. The advice my mother proffered then, ringing louder in my ears today, nearly four decades later, was: “For goodness sake, don’t support them – they will never support us.”

I became a Conservative, but that was before the Tories became such a small party. A small-minded party. A small-vision party, which is well represented by Theresa May. And now, a small party in numbers and increasingly representative of one age group. I left this party and joined the Liberal Democrats, a party big in heart and even bigger in tolerance. And a party big in ideas at the very moment Britain needs them most.

It cannot be incidental that some of the most important issues facing us today are about matters of freedom, liberty and choice. I think it profoundly wrong that the UK is the only country in Europe that locks up people without any limit on how long they can be detained. The government’s data protection bill purports to give us more control over our own personal information. However, buried in the details lurks another sinister intention. The intention includes an “immigration exemption”. This allows the government the power to remove data protection rights from anyone whose details are processed for “effective immigration control”. This is all May. She has created a nation where the burden of proof is now reversed: guilty until proven innocent.

May’s Britain was not voted for. She lost the last election when the voters took a closer look and said, “No, not you.”

I am fed up with this lot. I will do my utmost to make the small and extremely nasty party a bit smaller. Britain deserves the very best, and you, Mrs May, are not that. We all know it and I think you do too.

• Derek Laud is the author of The Problem with Immigrants and a former Conservative speechwriter