After a long wait and frantic calling to everyone, I finally managed to get a number to workpermits.gov.uk.
0114 259 4074
Surprisingly, its a normal landline. Alternatively one can reach them on
wpcustomers@ind.homeoffice.gsi.gov.uk
I guess most of the guys out there know this number/information.
Well, regarding my case, I got the information that, as long as I don't get my FLR stamp done on my passport and as long as my current company i.e. FIRM 'A' doesn't submit an end of employment form, which the companies should do when an employment is terminated/ends, I can stay back with my previous company, BUT, I should inform the new company i.e. FIRM 'B' that I am not taking up that job and they would intimate the Home Office/WorkPermits the same and the new WP gets cancelled and my earlier one becomes VALID. This is legal.
I can sleep peacefully now.
Now, one can ask, what if the new company (FIRM 'B') doesn't inform the WorkPermits/HO, about the cancellation? Well, I guess, its their duty just like its the duty of a company to inform the HO when an employment ends. But if they still don't inform and try to make trouble for you, you can approach a solicitor as your existing company didn't submit the end of employment, and fight your way through. They will be getting into as much trouble if they think of causing a problem. To be on the safer side, keep a copy of the letter/fax you send them stating that you are not joining them.
Hope this helps others who are in a similar situation.
Chris, its a one-way ticket, but it has a provision to return, till the point you go for your LTR stamp, provided your current employer hasn't submitted the end of employment form yet.