After a Sunday newspaper reported the prince drank six bottles of Smirnoff Ice - equivalent to nine shots of vodka - St James's Palace said Harry "had a couple of drinks".
The palace would not comment on allegations that traces of cocaine were discovered in toilets after Friday night's party, at Beaufort Polo Club near Tetbury in Gloucestershire.
In January Prince Charles ordered his younger son to attend a drug rehabilitation clinic, after Harry admitted smoking cannabis and taking part in heavy under-age drinking sessions.
'Not illegal'
Following the News of the World story a St James's Palace spokeswoman said the claims had been "blown out of all proportion".
She said: "He was at a private party and had a couple of drinks.
"He has not done anything wrong. He has not done anything illegal."
After Harry admitted drinking and smoking cannabis Prince Charles said he would be keeping a closer eye on him, to ensure there was no repeat.
The spokeswoman said: "His father and Prince William have certainly been around a lot more."
She would not say how Charles had reacted to the latest story.
And commenting on the allegations that cocaine was used at the party she added: "We are not aware that this involves Prince Harry."
Drug dealing
In February Prince Harry was told that he would not be charged after smoking cannabis and drinking underage at a pub near his father's Highgrove estate.
Wiltshire police investigated allegations of late-night drinking and drug dealing at the Rattlebone Inn, in Sherston, Wiltshire.
A police spokesman said no link had been found between the claims and Prince Harry.