In its annual monitoring report for 2010-11, published on 4 July, the Office for Fair Access remarks that "performance on widening access to the most selective institutions has been flat in recent years, despite their considerable efforts and investment".
The figures released by Offa show that only 1,385 students from families earning less than £25,000 a year (14.4 per cent of full fee-paying students) attended the University of Oxford in 2010-11, just 13 more than the previous year.
The University of Cambridge was the UK's least socially diverse higher education institution, according to the report, with only 12.8 per cent of students (1,411 in total) hailing from poor backgrounds.
Universities spent £424.2 million on widening access in 2010-11 - 24.4 per cent of the £1.74 billion received in tuition fee income above £1,310 a year - the current trigger for access regulation. Of the £378 million spent on scholarships and bursaries, £305.4 million went to the 322,000 students from low-income backgrounds.
About £46 million was spent on outreach - up from £39.6 million in 2009-10.
Access spending will rise to £621 million by 2015-16, with fee waivers, bursaries and outreach funded by £9,000 fees, Offa adds.
Sir Martin Harris, who will stand down as Offa's director at the end of August, insisted that the watchdog remained vital in the high-fee era because it challenged universities to do more on access.