Confidential documents have revealed the formidable lobbying operation waged by a tobacco giant seeking to undermine efforts to make cigarettes less attractive to children and women, and force packs to carry larger health warnings.

The documents obtained by the Observer show how Philip Morris International (PMI) employed 161 people to combat a proposed tobacco products directive (TPD), a major piece of European Union legislation that health campaigners say would save lives.

Under proposals by the commission's ENVI public health committee, which had been due to be voted on this week in the European parliament, cigarette companies would be forced to include large pictorial health warnings on tobacco products covering 75% of the front and back of packs. There would also be a ban on all flavoured tobacco products – such as menthol, vanilla and strawberry – and on slim cigarettes and slim cigarette packs. These are seen as particularly attractive to younger smokers and to women, say health experts. The directive could also lead to e-cigarettes being regulated under pharmaceutical legislation and sold like medicines, something some new entrants in the market oppose.

On Thursday it emerged that the crucial vote had been postponed by MEPs until 8 October, a significant victory for the tobacco lobby. As a result, time is running out to introduce the directive before January when the presidency passes from Lithuania, which is pro-regulation, to Greece, which is opposed to tobacco control.

"There is little time to get the directive passed before this parliament comes to an end and the whole process has to start again," said Deborah Arnott, chief executive of health charity Ash.

"That would be good news for the tobacco industry in its endless search to wring profits out of new addicts, but terrible news for children and young people across Europe."

Delaying the directive has been a key goal of the tobacco lobby. Internal PMI EU public affairs briefings from 2011 and 2012 – marked "private and confidential. For internal discussion and illustration purposes only" – show that the tobacco giant, which now employs David Cameron's election strategist Lynton Crosby as a consultant, was intent on derailing the directive.

In one slide dated 9 August 2012, PMI discusses whether its strategic objective is to "push" (ie remove elements of the directive) or to "delay" it. A company spreadsheet reveals that it used 161 employees and consultants in lobbying. It shows that in the year to June 2012, the lobbyists claimed almost £1.25m in expenses for their meetings with MEPs. The spreadsheet shows that by 22 June last year, 233 MEPs – 31% of the total – had been met by PMI at least once. In a separate spreadsheet, several MEPs are listed as having been met four or five times. Almost half of the European People's Party and European centre-right groups met with PMI's lobbyists, the documents show.

The internal slides also show how PMI targeted farmers' organisations, retail bodies and trade and business associations to reach high-level decision makers in the European parliament and the European Commission.

There is also evidence that the company commissioned academic and economic studies to promote its claims.

One slide showed PMI's intention to generate avis négatifs (negative opinions) about proposals put forward by the EC's Sanco directorate – the body charged with ensuring health and consumer protection.

Another slide explained that it was PMI's objective to ensure "that menthol be excluded from characterising flavours ban in TPD". PMI said it would not comment on the confidential documents leaked to the Observer. However, in a statement it said it believed the directive was flawed. "It is up to the EU to set the timeline for considering this legislation, and it is our hope that these flaws will be addressed and that the EU implements a regulatory framework that is fair, science-based and makes sense in light of the EU's priorities, without imposing unnecessary burden on the economy," PMI said.

Separately, emails released under the Freedom of Information Act by the Department of Health reveal that concerns about the directive were shared by other tobacco firms.

Earlier this year the department feared that Imperial Tobacco had obtained protected information from the European Council working group, which was helping draw up the directive.

The matter raised concerns in Whitehall that the tobacco lobby was in receipt of market sensitive information, raising questions about the relationship between Brussels and lobbyists.

Imperial wrote to the department to say it was alarmed to learn that in April the government had spoken in favour of plain packaging for cigarettes during a European Council working group meeting and demanded confirmation from the department.

When asked to reveal the source of its information, Imperial declined to tell the department.

The department was forced to write to Imperial explaining that the council's reports "are subject to principles of professional secrecy".