Tube strikes are expected t bring rush-hour chaos after the row over a sacked driver worsened.

Union bosses today announced four new strikes  – starting a week on Sunday – which threaten to severely disrupt services over seven days.

It marks the latest stage in a dispute between London Underground chiefs and Tube union RMT over the dismissal of driver Arwyn Thomas.

The strikes fly in the face of London Mayor Boris Johnson’s pledge to “fix” the Tube, which is beset by continuing delays and industrial disputes.

Johnson said he was “astonished” that the RMT had decided to announce strike dates before the outcome of employment tribunal hearing considering whether Thomas’s dismissal was fair.

The first strike is set to run from 9.01pm on Sunday 19 June until 3am Monday 20 June, leaving trains across the network out of place for the Monday morning rush.

This will be followed by walkouts from 9.01pm on Monday 27 June to just before midday the following day, crippling services during the Tuesday morning peak.

The third strike, designed to cause maximum disruption in successive rush-hours, starts at midday on Wednesday 29 June and runs for just under 24-hours. Finally, the fourth strikes runs from midday on Friday 1 July and ends that same day at 9pm.

The union had previously ordered five strikes, hitting services over 10 days, in protest over the sacking of two of its train driver members, Thomas and Eamonn Lynch.

Lynch was originally sacked over a train safety issue but was found to have been unfairly dismissed by an employment tribunal and reinstated into a non-driving job.

Union and LU agreed to hold talks over Thomas, whose own ongoing tribunal has been adjourned until the end of the month, and the strikes were cancelled.

Thomas was sacked for alleged “abusive behaviour” towards his colleagues. He denies the charge.

The union insists the “real reason” behind the sackings was because both men were admitted long-standing union activists.

Crow said today: “It is the intransigence of LU management, who have dragged their heels and failed to reach agreement over the past month, that has left us with no choice to put this strike action on.”

London Underground today condemned the strikes. A spokesman said: “It is completely mystifying that, having agreed with LU that the tribunal process should take its course, the RMT is now threatening strikes.”