from UCAS
Any statements showing a level of similarity of 10% or greater will be reviewed by members of the UCAS Similarity Detection Service team. HEIs will be notified of any cases where there are reasonable grounds for suspicion. Applicants will also be notified that the UCAS Similarity Detection Service has found that their personal statement merits investigation. The decision about what action, if any, to take regarding notified cases rests with the admissions tutors at individual HEIs.
HEIs are the unis applied to. Later it says
If Copycatch identifies a significant level of similarity in your personal statement and the Verification staff decide to inform the HEIs you have applied to, you will be notified by email, if you have a verified email address. This email will include instructions explaining how you can view the output of the detection program by using Track, including access to a frequently asked questions (FAQ) section giving advice and guidance.
The report sent to you is identical to the report sent to the institution. It will display your personal statement marked up to identify sentences similar to others in the Copycatch system. We use four colours (see below) to indicate significant matches with other statements and grey to show sentences which have not been found to match.
Within matched sentences, words in your sentence which are different from the one matched with it by the program are highlighted in black. Underlined black is used to show that the word is related but not identical.
What the sentence colours mean
Red is used for the sentences from the most matched statement.
Blue is used for the next best match if there are least 3 sentences.
Pink is used for the third best match if there are at least another 3 sentences.
Brown is used for any other matches if there are at least 3 sentences.
Grey is used for sentences for which no match has been found in the indexes and for very short sentences which don't get checked.
so it may be rather more serious than you're being led to believe by others on here.