Frederick Britten was an accomplice of Frederick Ward during his escape from Cockatoo Island and in the aftermath. A timeline is documented below. Further information is contained in my Fred Britten Blog Post and the deleted Fred Britten Chapter from Captain Thunderbolt and his Lady.
1863 Feb-Sep 20 Feb 1863: Frederick Britten (or Brittain, Britton &c. but Britten used throughout for consistency) arrived on Cockatoo Island. Born c.1836 VDL and arrived in NSW in 1845 perJulia (according to own statement but neither have proved possible to confirm – a brig Julia was sailing out of Tasmania at that time but only to Port Phillip and Adelaide); 1862: labourer; 5 Nov 1862: with George Willison and another robbed the Bathurst-Sydney mail (reportedly); 14 Nov: arrived in Sydney from Mudgee; 17 Nov: taken to police office for questioning after attempting to exchange stolen bank notes at the Union Bank; 18 Nov: returned to police office to collect his bank notes where Willison and wife were also being examined, and both men arrested; 19 Nov: brought before Bench of Magistrates and remanded; 20 Nov: admitted to Darlinghurst Gaol; 27 Nov: examined again; Nov: escaped from the police when being brought from the station-house in George Street across the yard to the Police-office (date unclear; Sub-Inspector Harrison at Feb trial said he was standing outside the court when Britten tried to make his escape); 12 Dec: committed by the Central Police Court to stand trial, and attempted to escape when leaving the prison van to enter Darlinghurst Gaol, with two horsemen nearby to assist, but escape unsuccessful and horsemen eluded the police; 6 Feb 1863 tried at Special Sessions of Sydney Supreme Court and found guilty (along with Willison); 9 Feb: both sentenced to 16 years servitude on the roads, the first year in Irons (probably because of his constant escaping); 20 Feb: transferred from Darlinghurst Gaol to Cockatoo Island; 5 Mar: John Ellis* visited Britten at Cockatoo Island; 30 Mar: discharged to Darlinghurst Gaol on Habeas Corpus to give evidence in John McCracken’s defence on a murder charge; 18 May: Mr Lane (who was he?) visited Britten at Cockatoo Island; 14/15 Jul: with mail robbery partner George Willison and two others attempted to break out of No.1 Ward during the night; 17 Jul: caught tampering with irons; 27 Jul: on both charges sentenced to 14 days solitary confinement in cells; description: 5’8”, slight build, fair complexion, brown eyes, long drooping nose, long light brown hair, small lightish whiskers, soft voice, smiling countenance; protestant; can read and write; Britten and Willison referred to as ‘flash, talkative rascals’ in the News and Notes by a Sydney man published in Brisbane Courier 
1863 Sep-Nov See Timeline: 1835-1863
1863 Nov + Nothing known with any certainty about Frederick Britten after November 1863 however see John Ellis* below
*John Ellis – 16 Apr 1863: apprehended on suspicion of being concerned in Bathurst mail robbery on 5 Nov 1862; 25 Apr: remanded until following Saturday; 9 May: Brought before Central Police Court, Sydney and acquitted as the witness failed to identify him however detained on suspicion of being escaped Victorian convict John Howard alias Anderson; Nov/Dec 1864: report that Thomas John Ellis alias Frederick Britten (plus other aliases) robbed a man at Jamieson, Victoria, was arrested and escaped from the Jamieson lock-up; Nov 1864: robbery of Mrs Garbutt at Cooyal by five men; Feb 1865: a John Ellis caught in Brisbane and remanded to Mudgee on Cooyal robbery charges (reports soon claimed that he was identical with Thomas John Ellis alias Frederick Britten who escaped from the Jamieson lockup however dates crossed over); further research needs to be done in Victoria’s Public Record Office
In attempting to work out the Britten/Ellis confusion, I made some notes (see Britten/Ellis jigsaw puzzle).
Also see the Fred Britten blog post and the deleted Chapter from Captain Thunderbolt and his Lady.
 Darlinghurst Gaol - Entrance Book: Frederick Britton [SRNSW 5/1896 Year 1862 No.2639; Reel 2338] & Darlinghurst Gaol - Description Book [SRNSW 4/6309 Year 1862 No.2639; Reel 860]; Cockatoo Island - Muster Roll: Frederick Britten, Feb to Sep 1863 [SRNSW 4/6508] & Cockatoo Island - Daily State of the Establishment [SRNSW 4/6505, 5 & 30 Mar 1863, 18 May 1863] & Cockatoo Island - Letter Book [SRNSW 4/6518] & Cockatoo Island - Punishment Book [SRNSW 4/6502 Year 1863 Jul 23 & 27]; Calender of persons tried on criminal charges in Sydney: Frederick Britton, 1863 [SRNSW 4/6450 p.148 No.2639; Reel 685. NRS 831]; Mudgee Liberal 7 Nov 1862 p.3, 14 Nov 1863 p.3 (x2); Sydney Morning Herald 13 Dec 1862 p.5, 16 Dec p.5, 17 Dec p.8, 7 Feb 1863 p.5, 10 Feb pp.3& 4, 3 Apr p.2, 11 May p.2, Argus 15 Dec 1862 p.5, 9 Feb 1863 p.5; NSW Police Gazette 1862 No.40 (3 Dec 1862) p.248; CSIL: Re Frederick Britten [SRNSW 4/508 Item 63/5091 No.63/4977]; Clerk of the Peace – Depositions for Sydney Circuit, 1863: Re Frederick Britten and George Willison [SRNSW 9/6449] ; Brisbane Courier 14 Feb 1863 p.3; Maitland Mercury 19 Sep 1863 p.5
 Sydney Morning Herald 27 Apr 1863 p.5, 11 May p.2; Vic PG 1864 No.46 (16 Nov 1864) p.366, No.51 (22 Dec 1864) pp.476 & 483; NSW Police Gazette 1865 No.12 (22 Mar 1865) p.113