Hi,first things first, you say it's a gas hob this should not be connected to a flexible hose, are you sure you are not talking about a free standing cooker one you can pull out and clean behind.
The problem sounds like the gas pressure is too low ,this could be due to pipe sizing or a blockage somewhere leading to your cooker. This needs to be checked by a CORGI reg person who will sort it by either by himself or he will get TRANSCO in to check your inlet pressure at the meter.
Please do not try to fix yourself unless you are qualified.
Hope this info helps you. Mic CORGI installer.