A 28-year-old man has begun a two-year six-month jail offending that left a 12-year-old girl "withdrawn, angry, and extremely self-conscious".

The girl's mother described the effects of the offending by James Christopher Middleditch, who touched the girl while she slept.

Christchurch District Court Judge Paul Kellar told him: "Offending of this nature affects everyone profoundly and for a long term."

He reduced the jail term for Middleditch's admissions to the police at his first interview, his early guilty pleas, and his remorse and steps towards rehabilitation.

But even with the reductions, the judge reached a sentence that meant home detention could not be considered.

Defence counsel Karen Chalmers had sought the home detention sentence so that Middleditch could continue with his rehabilitation.

Middleditch had interim name suppression when he entered guilty pleas in February, but Chalmers said there was no application for permanent suppression. However, an application for in-court photography was refused.

Middleditch had admitted two charges of sexual violation by unlawful sexual connection, and three charges of indecent assault on a girl aged under 16.

All the sex charges relate to the same victim, who reported waking to find the man touching her breasts, inner thigh, and groin area.

The girl's mother referred to Middleditch's "vile acts" and said his actions would have an immeasurable impact on the girl and her life ahead. Her daughter had been left withdrawn, angry and extremely self-conscious, she told the court.

She urged the judge to place Middleditch on the sex offenders' register - the prison sentence will ensure that happens.

Reports on Middleditch placed him at a low-to-medium risk of further offending, but the judge said he had been moved by the contents of the girl's victim impact statement and he regarded the harm caused as the main aggravating factor.