A walkout by Conservative London Assembly members has sparked a row about the stifling of open debate by City Hall's watchdog.

Conservatives members led by group leader Andrew Boff AM abandoned yesterday's assembly meeting, which passed a motion calling for London Mayor Boris Johnson to lobby government over the impact of welfare reforms on the capital.

The decision to exit the chamber was sparked when Mr Boff asked assembly witness Kate Bell, London campaigns co-ordinator for the Child Poverty Action Group, on Labour's alternatives to the spare room subsidy – more commonly known as the ‘bedroom tax'.

Mr Boff told The MJ he asked whether the Labour party's policy to apply tax after a home is given to the tenant would be an improvement on government proposals,

According to Mr Boff, chair of the London Assembly, Jennette Arnold AM - who proposed the motion - then instructed Ms Bell not to make a reply to a question she said should not have been asked.

Mr Boff said his group realised at that point they were not going to be allowed to ask ‘a reasonable question' and had no option but to stage a walkout

Mr Boff said it was ‘a travesty not to be involved in a debate on an important issue for Londoners' and complained the other three parties were effectively excluding  Conservative members and their constituents from having a full role in the running of the scrutiny body.