Former defence secretary Liam Fox, a Vote Leave supporter, said the proposals did not "come close" to the changes voters had been promised.
He said: "The very limited set of demands from our Government have been watered down by the EU in every area.
"The British people want to take back control and end the supremacy of EU law over our economy, our borders and our Parliament.
"None of these changes even come close to the fundamental changes promised to the public. We are being asked to risk staying in the EU based on the back of empty promises from the EU that are not even backed up in Treaty. The only safe option is to Vote Leave."
Brexit campaign group Leave.EU branded the proposals a "fudge and a farce".
Co-founder Richard Tice added: "We already have a 'red card' at the governmental level but are in a voting minority more often than any other EU member.
"Why should duplicating the process at the parliamentary level achieve anything besides making the EU even slower and clumsier in a crisis?
"We don't need a brake with someone else's hand on it, we need control of the steering wheel. Besides, planned increases in the minimum wage will attract more new migrants than benefits cuts will.
"We certainly don't need empty promises of an opt-out from 'ever closer union' in some future treaty after the referendum - it will evaporate even faster than our last promise on CAP reform did."
Ukip leader Nigel Farage said the deal was "hardly worth waiting for", adding: "It is truly pathetic. No treaty change, no repatriation of powers, no ability to control our own laws, our money or our borders. Now let's get on with the referendum.
"What it means is more Europe with an EU army, EU accession of Turkey, and EU primacy over our laws and our courts.
"Well, Cameron wanted a four-year ban on migrant benefits, he didn't even ask for a restriction on the open door movement that we have to nearly half a billion people. We can in the first few months or year stop benefits, but from years two, three and four bring them up to the current levels. This is pretty weak stuff."
He added: "There is no fundamental reform, there's some fiddling around the edges on migrant benefits. I absolutely predict that the effect of this will not be to reduce the numbers coming to Britain but given the huge increase that is coming to a minimum wage, to our living wage, even more people will come.
"I suspect the European Council will approve this document, they are giving us nothing."
Business leaders gave a qualified welcome to proposed deal, with the Institute of Directors (IoD) claiming it was "better than we expected".
IoD director-general Simon Walker said: "The top reform priorities for IoD members are to stop the flow of unnecessary red tape from Brussels, make clear the UK is not on a path to more political integration, and make the more EU competitive.
"There are proposals on these areas in Tusk's draft which hold promise, although no-one should get carried away just yet.
"Cutting back on pointless bureaucracy which stifles companies must be one of the top aims of these negotiations, so we welcome the commitment to scale back EU interventions in areas which should be left up to individual countries ... We were also pleased to see that the draft says the EU will put in place burden reduction targets for regulation where feasible.
"Politicians, wherever they are from, love making new regulations, so we need targets to counter-act this impulse. The targets must not be just where feasible, but wherever possible."
Mr Walker played down the importance of the "red card" proposal, arguing "frankly this is not likely to be used often, as it needs too many member states to agree".
John Longworth, director-general of the British Chambers of Commerce, said: "While Brussels-watchers will pore over every draft and every statement, most business people will want to wait to see a final UK-EU deal before assessing carefully the impact on their businesses and their vote.
"A lot can change in the weeks ahead. Like others, we will be evaluating these proposals against the Prime Minister's initial letter to Mr Tusk, and against the business priorities we have articulated."
Conservative MP and Foreign Affairs Select Committee chairman Crispin Blunt expressed concern about what would happen to the EU without a "good dose of British practical common sense".
"My position is marginally at the minute to leave but I am taking evidence - as is the FASC - as to what the implications for the UK are," he told BBC Radio 4's World At One.
"The negotiation is hitting a particular few pain points at the margin, but the major issues - about the size of our contribution, about the fact that we have agreed that our national parliament won't be sovereign in a very significant number of areas and whether the implications for that are positive or negative for the UK...
"The area that is causing me concern is just how bad would it be for the EU if we leave, and if the EU is a much weaker institution, much less able to resolve its conflicts with a good dose of British practical common sense at the centre of its counsels, how much of a problem would that be for a UK that was outside the EU.
"I don't think I have yet taken enough evidence on that to be confident of coming to the answer."
Graham Brady, chair of the Tory backbench 1922 committee, said he wanted "fundamental" change and still expected to vote for Brexit.
"I don't want to be churlish because I think David Cameron has clearly achieved some important improvements, but not on a scale that begins to address the concerns that I have," he said.
Foreign Secretary Philip Hammond, who is on a visit to Rome, said the EU had offered compromises that had previously been dismissed as "impossible".
"What this text shows is very considerable movement by the EU to recognise the concerns that Britain has set out in all four areas that the Prime Minister highlighted," he told Sky News.
Mr Hammond stressed the process was still ongoing, and it did not mean that the package was final.
"It does mean that in all four areas they are accepting that there can be movement and there can be a solution," he added.
Green Party MP Caroline Lucas (Brighton Pavilion) said: "Though I'm strongly opposed to Cameron's desire to water down EU regulations, it's clear that the vast majority of the protections we enjoy because of the EU will remain."
She added: "Taking away in-work benefits for EU citizens working in the UK is both unfair and unlikely to be effective. People who come here from other EU countries pay more in tax than they take out in public services.
"You won't hear it from Government ministers but the fact is that EU nationals are actually less likely to claim benefits than British people.
"Even in their watered-down form, Cameron's proposals will penalise those who contribute hugely to our society."
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