I thought that you meant to say that no penetration occurred, but I think that a word was missed in the typing.
First, to address the risk of each of the components of the encounter separately:
There is no risk of HIV or any other STD from kissing. The risk to the male for HIV transmission from unprotected oral sex is very low. It is so low that a specific numeric risk cannot be determined, but it is not zero. There is no risk of HIV from the penis touching the vagina externally. Penetration must occur for there to be any risk of HIV. So, the only component of this encounter that carries any risk is the oral sex.
And of course, any risk also is based on the prevalence of HIV in your community. The system says that you are in the UK, and in most communities in the UK, the prevalence of HIV in the female population is low.
So, since the only component that carries any risk is the oral sex, and the low likelihood that a girl of unknown HIV status would be HIV positive, it is not necessary to take PEP.
It is worth noting that while there is no HIV risk from the penis touching the vagina externally, there are some other STDs that can be transmitted by skin-to-skin contact, such as herpes and HPV/genital warts. However, there is no prophylactic intervention that can be considered for these infections. The only action that is needed is to monitor for any symptoms, and to be seen if any sores or warts develop.
If I can provide any clarification, please let me know.