Is a Practicing Certificate compulsory for all those who pass QLTT?

Whether or not you need a practicing certificate is a complicated issue. You should seek guidance from the Professional Ethics Division (professional.ethics@sra.org.uk) of the SolicitorsRegulation Authority (SRA).There is a booklet on the SRA’s website that deals with this issue and the link is:
http://www.sra.org.uk/documents/regulatory-framework/practising-certificate-regulations-1995.pdf

What is the Annual Fee to obtain a Practicing Certificate?

The standard practising certificate fee is £ 995, plus the Compensation Fund contribution.

Is there any concession to obtain a Practicing Certificate?

If your earnings were less than £ 20,000, you may qualify for a low income fee reduction. You may also qualify for a maternity leave fee reduction. You should seek advice from the SRA’s Information Services section on this matter.

Is it compulsory to renew the Practicing Certificate annually?

This depends on where you are based geographically, the type of work you are doing and if you are holding yourself out as an English solicitor. You should seek advice from the Professional Ethics Division of the SRA or read the guidance booklet -see above for the link and contact details