Lawyers waving placards and chanting blocked the road outside the Ministry of Justice on Tuesday evening in protest over proposals to slice a further £220m out of criminal legal aid and remove defendants' ability to choose a solicitor.

Prominent QCs and human rights groups warned that the reforms launched by the justice secretary, Chris Grayling, would destroy Britain's international reputation for fair trials and justice.

Several hundred protesters, chanting "No legal aid! No justice!" and "Stop the raid on legal aid", closed the road outside the entrance to the department near St James's Park in central London. Placards declared "One law for the rich", "Democracy under threat" and "Defend legal aid". Civil servants stared down from the ministry's windows above.

The demonstration was timed to coincide with the closing of the Ministry of Justice's (MoJ) consultation on "transforming legal aid", which solicitors and barristers specialising in defence work fear will undermine their livelihoods, deprive suspects of specialist legal help and increase the number of miscarriages of justice. Under the MoJ plans, the cost of judicial reviews will rise steeply, lawyers' fees will be slashed, and criminal legal aid contracts will be awarded through price-competitive tendering to the lowest bidder. Defendants on legal aid will no longer be able to choose their solicitor.

Among those addressing the protest were leading barristers such as Geoffrey Robertson QC, Dinah Rose QC and Michael Fordham QC, as well as human rights charities including Liberty, Reprieve and Kids Company. The shadow justice minister, Andy Slaughter, and MP David Lammy were present.

Michael Mansfield QC, who has represented the families of Stephen Lawrence, Jean-Charles de Menezes and the victims of Bloody Sunday, said: "None of this is primarily about lawyers, although they are affected. It is about a basic provision, justice, the very substance of what is left of our democracy.

"No fundamental rights are worth the paper they are written upon unless they can be enforced, especially against overweening and corruptive authorities.

"There has been, with small exceptions, an intransigence and almost dismissive contempt by government towards the plight of the citizen."

Rose, of Blackstone Chambers, said: "What on Earth is a Conservative-led government doing introducing a series of monopolies that are immunised from competition? It's contrary to the discipline of the free market."

James Welch, legal director of Liberty, said: "Squeezing out decent criminal practitioners will drive down standards and inevitably lead to miscarriages of justice. Meanwhile, the government protects itself from effective challenge by restricting legal aid for judicial review."

A series of damning submissions to the MoJ consultation were released during the day. The Bingham Centre for the Rule of Law said the plans would result in the "absurd prospect" of repeat offenders being represented by different law firms, and reduce legal advice to "the status of a commodity".

The Children's Society said the MoJ plans, which introduce a residency test, would deny legal assistance to "the most vulnerable young people", including those who have been trafficked or suffered domestic violence.

Citizens Advice said the latest round of cuts would be felt far beyond criminal cases and could be "the straw that breaks the back of universal justice".

The charity's chief executive, Gillian Guy, said: "If people simply can't talk to a solicitor as more and more firms are forced to close, then the knock-on effects could be devastating for everyone in society, not just the individuals facing charges."

Defending the proposals, Grayling has said: "At a time of major financial challenges, the legal sector cannot be excluded from the government's commitment to getting better value for taxpayers' money. We believe costs paid to lawyers through legal aid should reflect this. Professional, qualified lawyers will be available, just as they are now, and contracts will only be awarded to lawyers who meet quality standards set by the profession. Wealthy defendants who can afford to pay for their own legal bills should do so. We have one of the most expensive legal aid systems in the world, with about £1bn a year spent just on criminal legal aid. These changes are about getting the best value for the taxpayer, and will not in any way affect someone's right to a fair trial."