You just can't hope to pass the DSA practical driving test, you need to work hard, practice all the driving skills highlighted in the driving test requirements record, and be confident that you've done everything in your power to prepare. It is particularly important if you've already had an attempt at the test, that you don't stop taking driving lessons and just turn up at the test centre having only taken a hour tuition session on the day and think that you will still be able to drive at the test standard.
As a DSA approved assessor, I regularly see people who've failed a test, book another appointment with an examiner and only call me a week before the date asking for a 1 hour session a day or two before the test. In most cases their driving has gone rusty, and they make many driving mistakes, some of which they didn't even commit on their previous test, all because they haven't driven in the 8 week period since their last DSA practical car assessment! With only a short 1 hour driving lesson, it is not possible to make up for that gap, so the result is they go for the test and fail!
The video below shows an example of how people fail the driving test for not knowing how to deal with cars driving too close behind them.
You can't rely on lady luck to pass the test, 40 minutes is a long time and since you can be taken anywhere except the motorway, you can not fluke a pass as there are too many things that could go wrong if you have not practiced enough! Take the time to have enough driving lessons, and take a driving instructor's advice on what you need to work on, then you might have a higher chance of being successful and get that full british driving licence.
More practical test advice
Getting a guarantee of a driving test pass.