Media playback is unsupported on your device Media caption Alex Harris says she experienced "moments of panic" as she contemplated her future

British Greenpeace activist Alex Harris has said she felt so alone in a Russian prison that she communicated by tapping out messages on pipes.

Ms Harris, from Devon, said the code "kept her going" during the 23 hours a day she spent alone in her cell.

The 27-year-old was among 30 people held when activists tried to scale an offshore oil platform in September.

Ms Harris was released on bail but, along with the others, faces possible trial on charges of hooliganism.

The protest was aimed at an oil rig in the Russian Arctic owned by the energy giant Gazprom.

Initially the Russians charged the 30 people onboard the Greenpeace ship Arctic Sunrise - 28 activists and two journalists - with piracy, which has a maximum penalty of 15 years. The new charge has a maximum penalty of seven years.

Analysis When I sat down with Alex Harris, she was obviously still struggling to get over her two months in prison. She described sleepless nights, and difficulty in eating. She explained that she even found crowded shops stressful. Since the first time I saw her in the dock she has said that being alone in her cell 23 hours a day was the hardest thing. But when I asked if she and Greenpeace should have been more aware of the risks she was running by protesting against Russian Arctic offshore oil, she said that no-one could have predicted the Russian reaction.

Describing her time in a jail in Murmansk, where the crew were originally held, Ms Harris told the BBC she was initially "terrified".

"I didn't know where my friends were, what was going on, no-one could speak English and I couldn't communicate with anyone. I couldn't sleep, it was horrible," she said.

'Peaceful process'

She said she was not sure how she got through the first two weeks, where all she did was "sit there and worry and stress about the situation".

"Most days I spent 23 hours on my own - one hour was allowed for walking. That kept me going as we could shout to each other over the walls," she said.

It got better when she discovered her prison cell was next door to another activist.

"We managed to have some conversation on the radiator pipes - one tap was A, two taps was B. Sometimes it took 23 taps to get out one letter.

"Even though we couldn't see each other, it felt like we were together," she said.

But she said she still had moments of panic, especially when the detainees were moved to a jail in St Petersburg because she was scared of "the unknown".

She also told the BBC she feared a 15-year prison sentence might result in her not being able to have children.

But Ms Harris said she did not blame Greenpeace because no-one could have predicted what happened.

"In all of Greenpeace's history, nothing like this has happened.

"I thought the worst-case scenario might be that they'd bring us to Russia, that they could arrest us. I never once imagined I'd spend two months in a Russian jail for a peaceful protest," she said.

She described being bailed as a "positive step", but she said still was not free.

"It could drag on for a long time, I'm still nervous, I still have trouble sleeping and trouble eating," she said.

However Ms Harris said that even though it had been an "incredibly tough experience", she did not regret her decision to join Arctic Sunrise.

The other five British people who were arrested on the ship were: Anthony Perrett, from Newport in south Wales; Philip Ball from Oxford; freelance journalist Kieron Bryan; Iain Rogers from Devon; and Frank Hewetson from London.