Oct 6 (Reuters) - The following are the top stories in the Financial Times. Reuters has not verified these stories and does not vouch for their accuracy.

Headlines

Theresa May faces call to quit after disastrous speech http://on.ft.com/2xV6OrV

'Two-thirds' of Hammond's 26 billion stg budget war chest faces wipeout http://on.ft.com/2xVumNf

Royal Mail will use 'all legal options' to fight 48-hour strike http://on.ft.com/2xXwILk

Overview

Theresa May was facing growing calls from Conservative MPs to quit, as she returned home from Manchester on Thursday, but her party's rebellion was not yet large enough to oust her as Britain's prime minister.

Weak economic forecasts are derailing the UK's budget plans and as much as two-thirds of the 26 billion pounds ($34.04 billion) of headroom in public finances that Philip Hammond created last year as a buffer for the economy through the Brexit period is likely to be wiped out after the government's fiscal watchdog concludes its forecasts for growth have been too optimistic.

Royal Mail Plc has threatened to use "all legal options" to prevent the first nationwide strike since its privatisation, after the Communication Workers Union, which represents about 110,000 employees at the company, said on Thursday that it planned to down tools for 48 hours beginning at Oct. 19. ($1 = 0.7638 pounds) (Compiled by Bengaluru newsroom; Editing by Sandra Maler)