The end is approaching for this year’s London Film Festival for yours truly, but where there are films to be screened, reviews will be sure to follow.

One of the mostly hotly anticipated films at this year’s LFF was Martha Marcy May Marlene, a big hit at the Sundance Film Festival earlier this year.

The film centres around Martha (newcomer Elizabeth Olsen) who, when we meet her is running away from a remote commune in the Catskill Mountains. She manages to evade the other members before the intimidating Watts (Brady Corbet) catches up with her, but lets her go after Martha makes a plea for freedom.

With nowhere else to go, Martha calls Lucy (Sarah Paulson), the sister she hasn’t seen in two years. A relieved Lucy brings Martha back to the plush lakeside summer house she shares with her husband Ted (Hugh Dancy) and, evidently delighted to see her again, welcomes her back into her life.

Gentle questioning by Lucy as to where Martha has been the past two years brings the stonewalled reply that she was living with a man who lied to her. But it seems evident to Lucy that Martha isn’t being entirely forthcoming and has become more insular and unpredictable, fine one moment, withdrawn the next.

As Martha struggles to reacquaint to normal life with Lucy and an increasingly impatient Ted, we see through flashback how she was first introduced to the commune – made up mostly of young women and a handful of men – and to its charismatic, emotionally manipulative leader Patrick (John Hawkes, as quietly scary as he was in Winter’s Bone).

Lonely and vulnerable, Martha is renamed Marcy May by Patrick and after a period of uncertainty, including a deeply troubling moment when she is taken advantage of by Patrick so she can be ‘cleansed’, she slowly buys into the group’s dynamic and becomes indoctrinated.

Although the group espouses self-sufficiency, this doesn’t extend to some of them breaking into houses and helping themselves to whatever they can find. But when one break-in goes horribly wrong Martha is shaken to her core, presumably prompting her to make a run for it, although this is never clarified.

Haunted by her memories, which she can no longer rely on as being real or just delusions, an increasingly paranoid and unpredictable  Martha begins to suspect Patrick and the others have managed to track her down to the summer house, while an exasperated Lucy feels she can no longer help her sister and gradually accepts Ted’s suggestion to get Martha professional help.

An incredibly assured feature debut by writer-director Sean Durkin, Martha is your classic unreliable narrator, giving Martha Marcy May Marlene an uneasy, schizophrenic atmosphere from the start. Durkin isn’t afraid to make his central protagonist unlikable at times, and Olsen gives a break-out performance as someone whose emotional wiring is clearly on the blink.

The film’s conclusion is also likely to produce much debate – who exactly is in that car at the very end? Unless there’s a sequel it’s doubtful we’ll ever find out.

One of the things the festival has endeavoured to do in recent years is to actively promote new British cinema. Although the British film industry is in as healthy a state as it’s been for quite a while, the line-up of Brit flicks this time around didn’t appear that attractive.

One of the stand-outs in the lush festival guide was Junkhearts, the debut feature from Tinge Krishnan. Krishnan has certainly secured a top-totch cast, with Eddie Marsan (always a supporter of British film) and Romola Garai topping the bill, and rising star Tom Sturridge and newcomer Candese Reid filling the ‘exciting new talent’ quota.

Marsan is Frank, a ramshackle, broken ex-soldier living with a terrible secret from his time serving in Northern Ireland, who can’t see beyond his next bottle of whiskey.

While stocking up on his daily drink fix at his local off-licence he encounters Lynette (Reid), a mouthy teenager  sleeping rough. Frank initially ignores Lynette, preferring not to get involved, but when he comes across her for a second time a connection between the two is made and, taking pity on her, he invites her back to his unkempt tower block flat to get some rest and clean herself up.

Meanwhile, in another part of London, Christine (Garai) is trying and failing to juggle a high-pressure job, drug habit, affair and motherhood. Christine seems to sleepwalk through her life, just like Frank. But Frank is woken from his self-destructive slumber by the paternal affection shown by Lynette and for a moment there is hope.

However, that chance of redemption for both Frank and Lynette quickly evaporates with the arrival of Lynette’s rotten, drug-dealing boyfriend Danny (Sturridge). Soon the flat has been taken over and turned into a drug den, while Frank retreats to the bottle.

But when a second chance to save himself and Lynette materialises, will Frank be able to keep himself together long enough?

For a film that is so unremittingly bleak for large portions, there has to be a hook on which to keep the audience invested and that hook comes in the form of the performances of Reid, Sturridge and Marsan, all of whom are terrific. And to the film’s credit you’re kept guessing as to whether Frank will be able to come good in the end.

Also, hats off to Krishnan for showing a more realistic, grittier side of London – there are no picture postcard shots of the Houses of Parliament or the Gherkin here.

However, the whole plot strand involving Christine simply doesn’t work and Gorai is wasted in a role that’s paper-thin and only there to service a suitable emotional pay-off at the end. You’ll also work out pretty quickly what the connection between the seemingly disparate plot threads are.

Krishnan shows promise though and, with a slightly better script it will be interesting to see where she goes next.