From today 1st September, mandatory overseas criminal record certificates are required for all applications. "if you are applying for entry clearance as a Tier 1 (Investor) or an adult dependant (over 18 years old) of the main applicant in this route, you must provide an overseas criminal record certificate for any country you have resided in continuously for 12 months or more, in the 10 years prior to your application.
You must provide the following specified documents:
The original certificate, for each country (excluding the UK) where you have resided continuously for 12 months or more in the last 10 years, since aged 18 years old, issued by the overseas authority, and
If the original is not in English, then you must provide a translated copy of certificate, in line with the requirements set out at: www.gov.uk/certifying-a-document. "
Certificates will only be considered valid if they have been issued within 6 months of the visa application or within the expressed validity period of the document, whichever is the shorter. If you are unable to obtain a certificate, for example because the country does not produce such documents or because of any other reasons, you must provide a letter which details your attempts to obtain a certificate and confirms why this has not been possible.
If you fail to provide any certificates or an acceptable explanation your application will be refused under paragraph 320 (2A) in the General Grounds for Refusal, Part 9 of the Immigration Rules. If you provide false or fraudulently obtained certificates your application will be refused. You may also be subject to a 10 year ban for any future entry clearance applications.
Amended guidance effective from 1st September here.