I am replying as a course writer - this is not an official CTHA reply.
Mindfulness is not on the list of qualification therapies on the CTHA site, so you should gather course information and ask the office directly.
You would probably be ok with the NCFE Level 5 Mindfulness and CBT course distance learning course from Stonebridge (written by me), BUT you will need to also complete the practical training approved by the insurer (same insurer as used by CTHA) to permit you to be classed as practical trained. CTHA is rightfully not fond of distance learning, you need to ensure you do the practical training and case studies, since this combines to make you more acceptable as a well rounded practitioner. You should check first by emailing the office via the CTHA contact page. If you need course content details and hours of practical training details, email me at email@example.com I can then provide the full details for you to ask the office and double check it is approved / approvable. I am happy to help and give the office any info they need to make their decision.
other than that I am aware of post graduate awards at Bangor University and Aberdeen University. For these though you are looking at around 3 years of post graduate study with the associated high university fees. They are both great courses though!