A principal target for the prime minister in his speech on Europe will be to wrench the UK away from the social and employment policies of the EU. Millions of people in Britain will suffer if he is successful. He must not be.

The Conservative party has never liked the European Union social dimension. New Labour signed up to the social chapter, but it was subsequently lukewarm about it. But it did enact new EU-based laws on agency workers' and consultation rights.

Europe's trade unions believe that if the single market is to enjoy popular support, it must have good employment standards. The ambition to achieve this has been around since the start of the EU and was accelerated under the presidency of Jacques Delors. Under him, Europe's leaders agreed that the single market should not allow competition on the basis of one country using poor health and safety standards to gain an advantage. Margaret Thatcher signed up to that principle. As a result, EU legislation on health and safety has spread high standards throughout the Europe. In this field, the UK has been the country to follow, and our regulations form the basis of the EU directives.

It is this legislation that underpins the controversial working time directive, a particular bete noire of David Cameron. This provides for a normal upper limit of 48 hours on weekly working time, regular rest breaks and four weeks' paid holiday. Sadly, in my view, the UK already has an opt-out from the 48-hours rule, so the key provision that does apply here is the four weeks' paid holiday entitlement. Is Cameron proposing an end to that? It was a big step forward for millions of British workers.

Following the Maastricht treaty, "social" Europe expanded, despite another UK opt-out, this time from the treaty's social chapter. EU leaders (minus the UK) agreed that the single market should aim to minimise competition based on the cheapness and vulnerability of employees. They accepted the trade union argument that decent labour standards must apply to avoid a downward spiral of pay and conditions.

So far, millions of British workers have reason to be grateful for EU employment measures. Part-time workers get equal treatment and pay. So do temps and agency workers. Employees whose company changes hands keep the same conditions with the new employer. Equality for women and minorities is a central condition. A voice at work is provided in very large companies by more than 800 European Works Councils, for example in BAE, Rolls Royce and Unilever; and in smaller work places, by new rules on information and consultation about change. Migrant workers get equal treatment, which also helps protect the pay and conditions of British workers from being undermined.

If the prime minister renegotiates us out of "social Europe", all these gains are at risk. You have only to look at what the government is doing now to rights that derive from the UK. Its current agenda includes new restrictions on access to tribunals by requiring cash deposits and raising qualifying conditions; cuts in legal aid and available compensation; shorter periods of notice of redundancies; and encouragement to sell rights for potentially worthless shares. Already 3 million workers have been taken out of unfair dismissal protection.

The EU's employment laws are bulwarks against more raids by the government. That is why the Conservatives hate them so venomously. These laws are not making the UK less competitive. In fact, by raising standards, they're a spur to higher productivity, investment and skills. Without them, our future could be a race to the bottom in the single market.

Cameron's manoeuvre is unworthy and mean-spirited. EU employment rights, like the EU itself – even with all its flaws – deserve the determined support of British working people. They're a cause worth fighting for. His vision of a UK without significant protections for employees, and competing not on quality but on cheapness and vulnerability, would be a disaster.