When Conservative MP Harriet Cross runs the London Marathon on Sunday, she is hoping to hit the finish line well within four hours.

If she can get there in under three hours 57 minutes, that would make her the fastest female MP, beating a record currently held by Jo Swinson, Liberal Democrat leader in 2019.

Cross is aware of the record, but is not counting her chickens.

“There is a 26.2 mile course between me and that at the moment, so I don’t need to get ahead of myself,” she says.

“I’m hoping for something in the three hours mark, but we’ll see how it goes on the day. Mid-three hours would be a happy result.”

The MP for Gordon and Buchan is an experienced runner – in 2023 she won a 50km (31 mile) ultra marathon – but still admits to a bit of nervousness about London.

She has done plenty of mountain marathons, but this will be her first on a road surface.

“This is different because it’s flat… when you’re going up a hill you get to walk, so this is a lot more daunting.”

And then there are the crowds. In Scotland, where she usually runs, she says there are normally a few hundred people gathering to watch.

Running in front of 50,000 people will be “daunting”, she says.

For Labour MP Cat Smith, Sunday will be her third London Marathon, yet she also has a few nerves.

She says she is “fully diagnosing” herself with “maranoia” – the anxiety and fear that can hit a runner as marathon day approaches.

“The last few days before you do the run you start thinking back to all the training runs and thinking ‘maybe I should have done another one, or maybe I should’ve tried harder or worked harder, and maybe I need to go back to the gym and do a few more weights because are my knees really strong enough?’.

“You start questioning everything, but I think that’s totally normal and I recognise that from previous times,” the Lancaster and Wyre MP adds.

Unlike Cross, she is not looking to break any political pavement pounding records. Last time, she managed six hours six minutes.

“I’m incredibly slow – I am the tortoise who will get there in the end,” she says.

“When you compete a marathon, that is the real prize.”

As an experienced London Marathon-er, does she have any words of wisdom for her fellow parliamentarian?

“I have absolutely no advice at all that is worth having. Just keep one foot in front of the other,” she says.

The pair will be among 16 MPs running the race on Sunday – and Cross thinks there are some parallels between running a marathon and a political life.

“It needs determination, needs focus. You need to not be distracted by what other people are doing around you,” she says.

“If you go off at the start of the marathon with someone who is trying to get a two thirty and you’re nowhere near, that you’re not going to get very far.”

Cross is raising money for Kayleigh’s Wee Stars, a charity that raises money for families of children who have terminal illnesses.

Smith is running for the Bay Hospital charity, which she says raises money for the “nice extras” that the NHS doesn’t provide, as well as some medical equipment.

You can listen to the interviews on BBC Radio 4’s Today in Parliament at 23.30 BST on Friday and after that on BBC Sounds.