The Guardian reports:
The loyalist group claimed it had been exploited and manipulated by MI5, MI6 and British special forces from 1972 to 1978 and again in 1985.
“In 1985 we were approached by a MI5 officer attached to the NIO [Northern Ireland Office] and based in Lisburn,” the UVF letter said. “He asked us to execute you.”
Justice for the Forgotten, which represents victims of a number of cross-border loyalist attacks, has since been into the National Archives in Dublin to view the letter, and reports additional details in a Facebook post today:
The letter purportedly sent by the UVF (M.U. unit, Mid-Ulster?) to Charles Haughey, dated 5th August 1987, begins by claiming that Colin Wallace and Fred Holroyd were telling the truth about British Intelligence bring 'behind killings, kidnappings and a smear campaign against Haughey.'
The author says they were given photos of IRA men and were provided with explosives and they killed 17 men on information supplied. (Read the full post)
Clearly, it is early days in assessing the provenance of this document, but despite the letter's spelling errors, the accounts above imply something sophisticated enough that a hoax would raise significant questions of its own.
The timing might suggest one motive for the UVF to produce such a letter. In August 1987, unionist relations with the British Government were still at a low point as a result of opposition to the November 1985 Anglo-Irish Agreement. So much so that both the Ulster Unionists and the DUP were still boycotting British Government Ministers at the time.
The UVF enjoyed a resurgence as a result of the backlash, and Aaron Edwards' recent history of the organisation suggests that it was receiving political advice from a high-profile unionist figure on the agreement's implications . The DUP's paramilitary wing, Ulster Resistance, was also conspiring with the UVF and the rival Ulster Defence Association to import arms.
The UDA definitely was being manipulated by British intelligence at this period. Army agent handlers recorded a meeting with the UDA intelligence officer Brian Nelson on 4 August, a day before the date of the UVF letter, and Nelson's journal suggests that they passed on targetting information at another meeting a few weeks later .
The UVF, or elements of it, may have seen exposure of similar activities as a way to drive a wedge between the British and Irish Governments and so undermine the Agreement. Such a propaganda purpose might involve deception, but would also require sufficient credibility to convince Irish officials. While it is not the only conceivable explanation, it is not therefore implausible that the letter is authentic, and its contents require further serious examinaton.
Update: The letter has now been posted by Justice for the Forgotten, and is attached below.
 Aaron Edwards, UVF: Behind the Mask, Merrion Press, 2017, p.183.
 Sir Desmond de Silva, Volume 1 - Chapter 7: The activities of Brian Nelson 1987- 89, Pat Finucane Review, 12 December 2012.