Info from TfL:
https://tfl.gov.uk/modes/tube/tube-strike

"If the strike goes ahead, there will be no Tube service from late
afternoon on Wednesday 8 July and no Tube service at all on Thursday 9
July. All other public transport services and roads will be much busier
than usual, so please check before you travel."

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Might actually happen. The turnout in the ASLEF strike ballot was high,
as were the votes in favour of a strike - 98% yes on an 81% turnout.

Not sure the RMT has stated what its strike ballot turnout was, but
91.8% voted to strike.

The TSSA meanwhile had 76% in favour of a strike on a 44% turnout.

The ASLEF turnout of course more than meets the government's proposed
50% turnout rule for a strike ballot.

http://www.theguardian.com/uk-news/2015/jun/18/london-biggest-tube-strike-10-years-night-shift-pay

http://www.cityam.com/219122/rmt-workers-vote-strike-over-night-tube

http://www.bbc.co.uk/news/uk-england-london-33331660

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Also from this FT article - "Last-ditch talks aim to head off London
Tube strike":
http://www.ft.com/cms/s/0/1c794e50-23bc-11e5-bd83-71cb60e8f08c.html

---quote---
The 24-hour walkout on Wednesday evening would cause the most widespread
disruption on the capital’s Tube network in more than a decade. Most
strikes in recent years have largely involved station workers rather
than Tube drivers.
---/quote---

Though think that must refer to strikes that actually happened, rather
than those which were just threatened. There were also strikes by
infrastructure workers too a few years back.