Does anybody know that how many weeks required to attend in pre-sessional course in the event of holding 6.5 IELTS point or 7

many thanks

They do not have any strict requirements. It is up to you - to take 12 weeks pre-sessional course or only 4 weeks pre-sessional.

UCL Language Centre states, that they expect their students to improve their IELTS score for 0.5 points every 4 week.

This may mean, that if you have 6.5 scores on IELTS, they ADVISES you to take 8 weeks course. If you scored 7.0, they ADVISES you to take 4 weeks course.

And the general advise - in case of such questions, it is always better to contact the university language centre directly. Do not rely on forums!

many thanks for your reply. it had better send my ielts certificate without waiting to achieve 7.5.