I finally segregated the two troublesome Guppies:
Segregated the Guppies
We were out most of the day visiting friends and on returning discovered they had escaped through the netting.
I then had the remove them from the tank itself.
We're returning them back to the pet shop today.
I have a 64 litre tank:
Photos of my aquarium
I originally introduced the following tropical fish:
5 Neon Tetra
1 Peppered Corydoras
1 Platy
The above have lived in the tank quite peacefully without any issues.
Yesterday I added 3 Guppies and two of them have been chasing the Platy around...