This government has embarked on one of the most aggressive programmes of welfare reform Britain has ever seen, and we already have a proud record of achievement. There is no doubt that changes to the welfare state are desperately needed. Our reforms will put an end to people being left on sickness benefits year after year; they will eradicate the trap that has left so many better off on benefits than in work; and they will ensure the benefits bill is sustainable over the longer term.

Questions have been raised about whether the dramatic pace of our reforms is too difficult to implement. But these doubts ignore my department's proven track record of delivering change and show a lack of ambition from the people raising them. Look at what has already been achieved.

We promised a benefit cap and it began, on time, in April in four London areas. It will be completely rolled out by September. We introduced the new personal independence payment as planned and on time. Automatic enrolment started last year, and now 1 million people have been registered into a workplace pension. People are using our Universal Jobmatch website for more than 5m job searches a day. Our Work Programme has launched and the industry tells us that so far 321,000 people have found a job through it.

I am proud of this record. But my main concern about the delivery of our reforms is that we bring them in safely. I have no desire to follow in the disastrous footsteps of the last Labour government and rush out changes to meet an artificial timetable, only to be forced to scramble to sort it out when it goes wrong.

Universal credit, which is the centrepiece of our reforms and will bring six benefits and tax credits into one, is following a different approach. We started it six months ahead of schedule, in April, in Greater Manchester and Cheshire. The first claims were taken in Ashton-under-Lyne jobcentre. We then expanded to Wigan jobcentre at the start of this month, and from Monday new claims will be taken in Warrington and Oldham. This approach allows us to forensically understand how everything is working, what might need to change, and what support people need to manage. I make no apology for it.

From October we start the national rollout of universal credit. Six new jobcentres will begin to administer new claims. At the same time, we will launch the elements of universal credit that will help bring about the cultural transformation of the new benefit. All jobseekers will sign on with a "claimant commitment" that spells out what they will have to do in order to get their benefit.

Universal credit is a fundamental change. I don't pretend otherwise. People who claim it will experience something very different from the current system and that's why I will ensure we have it right before it rolls out far and wide.

I find it nothing short of amusing that the opposition is now calling for universal credit to be delivered faster. While I welcome its support for this radical transformation – following its rejection of all our other reforms – I won't take lessons from a party that brought us tax credit chaos and oversaw the decay of the welfare system.

In opposition it has been the same old Labour party. It has opposed £83bn worth of welfare savings, voting against universal credit, voting against the benefit cap, all our much-needed welfare reforms. Even Labour's paymasters, Unite, overwhelmingly support the benefit cap; the union agrees with us that nobody should be able to earn more in benefits than the average family earns going out to work. But Labour opposes this principle. The welfare party is in a mess. They spent 13 years letting the rot set into the welfare state, and I am now busy putting things right.

I don't apologise for attempting to do what previous governments have shied away from, bringing in major changes to make the welfare state fair to both the people who use it and the taxpayers who pay for it. We have been ambitious and will continue to push ahead with these reforms, but we will do so in a safe and responsible way.