There are a couple questions here, so I'll address them separately.
Does British Sugar provide Marijuana to GW Pharmaceuticals from a 45 acre cannabis farm?
Yes, however the amount of land being provided to GW Pharmaceuticals is an insignificant portion of the actual land that British Sugar uses to grow crops, and likely has little impact on its bottom line. Furthermore, Ms. Atkins has removed herself from discussions and policy making involving marijuana.
The Telegraph reported back in 2016 of a business deal between British Sugar and GW Pharmaceuticals to provide exactly that.
British Sugar will be swapping tomato plants for cannabis seedlings after signing a long-term contract to supply the crop to drugs company GW Pharmaceuticals.
The marijuana plants, which are of a non-psychoactive variety, will be grown in British Sugar’s 18-hectare glasshouse in Wissington, Norfolk, where the company, a subsidiary of Associated British Foods, is currently cultivating tomatoes. The space is the equivalent of 23 football pitches.
“Every year we try to work out the best commercial assets for the glasshouse,” said Paul Kenward, managing director of British Sugar.
(Note: 18 hectares is approximately 44.5 acres)
Peter Reynolds, president of Clear, Campaign for Cannabis law reform, has called out Victoria Atkins for her behavior.
[W]hat is appalling is she doesn't just want to support it for policy reasons, quite evidently, she wants to support it because her husband and family are directly benefiting from [the regulation of] it.
However, this seems to be directly contradicted by Ms. Atkins' behavior with regards to marijuana legislation. She directly declared a conflict of interest and excused herself from any debates regarding marijuana policy.
A Home Office statement said: "In 2016, British Sugar was granted a Home Office license to grow a non-psychoactive variant of the cannabis plant.
"Victoria Atkins MP declared this fact in parliament when speaking in a debate as a backbencher, when she was appointed as Minister for Crime, Safeguarding and Vulnerability in November 2017, the Minister voluntarily excused herself from policy or decisions relating to cannabis, including licensing".
(...)
Speaking in parliament in July last year, she said: "I must first declare an interest, because my husband works for a company that has a license to grow non-psychoactive versions of cannabis to treat epileptic conditions in children.
Regardless, the deal between British Sugar and GW Pharmaceuticals is an almost insignificant amount for British Sugar. While there are no exact numbers in terms of the deal between the two companies, we can compare the amount of land used to grow marijuana to the total land used by British Sugar.
In their 2015/2015 annual report, British Sugar claims 60% of all sugar consumption in the UK, and claims over 100,000 hectares of land devoted to the growth of sugar beet. Now, it is unclear if the 100,000 is used primarily by British Sugar, or if it is only 60,000, but that amount of land use dwarfs the 45 hectares being devoted to marijuana growth for GW Pharmaceuticals.
Does Capital Group have a link to GW Pharmaceuticals?
Yes, but the link is extremely weak and not notable at all. Furthermore, Philip May has no impact on investment decisions.
On 19 June 2018, Yahoo Finance reported that Capital Research and Management Co. owned 13.31% of GW Pharmaceuticals. They are not even the largest shareholders in GW Pharmaceuticals (Scopia Capital Management LP owns 13.62%), much less the majority shareholder.
In addition, GW Pharmaceuticals is not a significant portion of their total investment portfolio. Nasdaq.com reports their holdings into GW Pharmaceuticals as the 140th largest position that Capital Research and Management holds, representing a grand total of .13% of their total holdings.
Capital Research and Management was reported by Bloomberg as a subsidiary of the Capital Group Companies. There seems to be some confusion as to which company Philip May works for, but he does not work for Capital Research and Management.
His Wikipedia article reports that he works for Capital International, another subsidiary of Capital Group. Capital International is located in the United Kingdom so it would make sense that Philip May works for them; however, I cannot find a source beyond Wikipedia. CNBC reported that he worked for Capital Group as a relationship manager.
Regardless, according to Capital Group, Philip May does not make decisions involving financial transactions and investing.
A Capital Group representative confirmed Philip's position at the company, explaining that he works with U.K. clients to ensure "they are happy with the services being delivered...and that we understand their goals. Philip was not involved with our investment research or portfolio management activities."
Regardless, the article tries to make a connection between Theresa May and GW Pharmaceuticals. Once context is injected, the claim can be accurately described as follows:
The husband of the Prime Minister of the UK works as a customer relationship manager for an investment firm whose subsidiary has one tenth of one percent of its assets in a pharmaceutical firm that is making a drug based off cannabis.
