The summer holidays is the longest period that pupils are away from their teachers in the academic year. It is also the time period that their academic studies may jump the most / make the biggest leap forward. This is especially true for the gap between GCSEs and A-level subjects where students are expected to complete more independent study and read around each topic themselves.
Learning a new language is particularly hard as it is. Let alone if you take a month and a half break from your studies.
To be comfortable listening, speaking and to perfect your accent, a new language learner should engage in conversation in the language on a regular basis. This could mean holding a conversation with a native in the language every so often but if you are particularly struggling, a tutor will be able to have those conversations with you and also critique you to help you progress.
A tutor throughout the summer holidays does not have to be used for a specific school subject. Many tutors offer valuable skills to help with your academic journey too. For example, exam technique, essay writing and even help with your UCAS application and personal statement.
If you are starting a new subject at A-level, or you know that your current chosen subjects are about to ramp up in difficulty after the break, it is worth finding out which topics you will cover next year and then evaluate how hard each topic might be. This way you will find particularly difficult and alien-to-you topics early on when you have time to do something about them. You have time to read around the subject and get an understanding of the basics before you are thrown back into the school environment. You could even hire a tutor for a few introductory sessions.
Particularly for complex subjects like Chemistry and Maths where certain topics can take a long time to get your head around but prior reading can make a huge difference in the speed you are able to pick up and master the new topic.