In UK trade mark law, it is well established that small differences in short marks are more noticeable, making confusion less likely. However, as shown in the recent CKA decision (Calvin Klein v Guangzhou Xika Technology (O/0724/25)) this principle is not absolute. Where the earlier mark enjoys a strong reputation, the UKIPO may still find confusion.

Various UKIPO decisions have applied the general “short mark” principle. For example:

• MOBO v MOTO (O/431/02) – where a one letter difference between two short marks was considered significant enough to avoid confusion.
• RASE v RABE (O/0256/24) – similarly, where a one letter difference in a four letter mark was held to be more significant than in a longer mark, leading to no confusion.

However in each of those cases, there was no successful reputation claim, so the decision turned purely on the visual and aural differences between the marks.

The recent decision in CKA reinforces how reputation can override the short mark principle.

The opponent, Clavin Klein, relied on its well known “CK” mark to oppose “CKA”. The UKIPO acknowledged that consumers would notice the extra A, which would normally be enough to avoid confusion. However, Clavin Klein proved a reputation in CK, meaning that consumers were still likely to perceive CKA as a sub brand or otherwise linked. This led to findings of indirect confusion and unfair advantage under sections 5(2)(b) and 5(3) TMA 1994.

Without reputation, small differences in short marks can be decisive. However, with a strong reputation the differences may not prevent a finding of confusion.

For applicants, this goes to show that you should not assume that a one letter difference will be enough if you’re up against a famous short mark. And for the owners of those famous short marks, evidence of reputation can be a powerful tool to overcome the usual short mark reasoning.