From his website – there is no date but probably just before bin Salman’s visit to UK in March 2018:
“Visit to the UK by the Crown Prince of Saudi Arabia, Mohammad bin Salman
The Government expects the visit to usher in a new era in bilateral relations focused on a partnership that delivers wide-ranging benefits for both the United Kingdom and the Kingdom of Saudi Arabia. The Government intends to enhance our co-operation in tackling international challenges such as terrorism, extremism, the conflict and humanitarian crisis in Yemen and other regional issues such as Iraq and Syria.
I am aware that Vision 2030, a programme of internal reforms, has been set in motion in Saudi Arabia by the Crown Prince. These include lifting the ban on women driving from June this year, opening up attendance at major sporting events to women and allowing cinemas to operate in the country. Vision 2030 aims to catalyse and open up the country’s economy over the next 15 years, which will provide opportunities for British businesses to help support delivery in areas such as education, entertainment and healthcare where they have world-class expertise.
It is my view that maintaining a good relationship with Saudi Arabia allows us to support their important programme of reform, and to have frank conversations on matters where we both have concerns. It is for this reason that I did not agree with the petition to prevent the Crown Prince of Saudi Arabia from visiting the UK.
Additionally, as the Chairman of the Conservative Middle East Council (https://cmec.org.uk) I am committed to improve our understanding of the threats, challenges and opportunities in the Middle East which as you will be aware is a complex but important part of the world.”