Tuppence Middleton has been battling "devious, nimble little beasts" in her brain for three decades

In an extract from her upcoming book 'Scorpions' obtained by MailOnline, she wrote: "My mind is full of scorpions. Devious, nimble little beasts that have occupied my head for the best part of 30 years ...

"It is leaving the house that presents me with the biggest challenge.

"In the midst of my obsessive thought cycles, I might send a quick message to my agent/friend/family member to say I am running late. Transport issues, I'll say. Then I start my counting to eight routine again.

"Close and lock the front door. Pull at the door's handle for a count of eight, to make sure it is firmly closed. Push against the door for a count of eight, to make sure it can't be pushed open. Pull the door for a count of eight. Push the door for a count of eight. Pull the door for a count of eight. Push the door for a count of eight. Pull the door for a count of eight. Push the door for a count of eight. Continue until I am satisfied it is closed.

"I have begun to rely on a fairly simple coping mechanism: taking photographs.

"I have an online photo album that is forever in a state of full capacity due to the excess of mundane domestic photography I insist on housing there.

"I take and keep photographs of doors, ovens, locks, fridges, windows, lamps, candles and plug sockets, with the sole purpose of calming my anxious future mind."

As well as OCD, the 37-year-old star revealed she has a fear of vomiting, and it was her panic attacks that made her go and see a doctor, who got her to undergo a course of cognitive behavioural therapy (CBT).

She admitted: 'I arrived utterly convinced that before the course was finished I would be forced to place both hands on the inside of a toilet bowl and made to lick them clean in order to expose myself to a level of bacteria so high that I would become violently sick and in turn address my fear of vomiting.

"None of this subsequently happened, of course, due to the fact that, first, exposure therapy was never mentioned in our sessions and, second, because I did everything in my power to convince my therapist from day one that I was recovering at a rate of knots."