By Charles Haviland BBC News, Colombo

	UNP leader says minister's behaviour flouted Sri Lanka's constitution

Government workers have also expressed outrage and say they will launch a nationwide protest campaign on Thursday.

The controversial deputy minister, Mervyn Silva, punished the man for not attending a programme on controlling the mosquito-borne disease, dengue fever, which has killed scores of Sri Lankans this year.

Mr Wickremesinghe said Mervyn Silva's behaviour flouted the country's constitution by bringing intentional harm on others.

A big public-sector trade union says it will stage protests outside government offices all over the island and will also suspend its own participation in programmes on dengue fever until disciplinary action is taken against Mr Silva.

Ruling party 'no comments'

A governing party official said Mr Silva's behaviour did not reflect the party's position but would not comment further.

Local websites have carried pictures of the hapless welfare official tied to a mango tree by Mr Silva.

Public-sector unions they will suspend its own participation in programmes on dengue fever until disciplinary action is taken against Mr Silva

The ordeal lasted 10 minutes and came after Mr Silva accused the man of not attending meetings to help tackle dengue.

The man in question said, however, that he couldn't take part as his child was ill.

Dengue fever, carried by mosquitos which breed in stagnant water, is a serious problem here.

It has killed more than 160 people this year and has made more than 22,000 ill.

However trade unionists have condemned Mr Silva’s form of direct action, calling it “unacceptable”.

Mervyn Silva, who is deputy highways minister and is highly influential in a Colombo surburb, once invaded Sri Lanka’s national TV station with a band of supporters and had to be expelled.

He is one of the most controversial figures in Sri Lankan politics and, through this latest act, has lived up to his reputation.