The policies arranged by the LTA for registered venues and accredited coaches provided under coach accreditation are public and employers liability (which protect you if you are sued by someone else for causing injury to them). Accredited coaches also have personal accident cover (which provides specific benefits to you if you suffer an accidental injury whilst coaching). These policies do not provide cover in respect of the commercial impact of a pandemic like Coronavirus.
If you have a business policy it is possible that the business interruption section of that may provide some cover, depending on the policy wording and the specific circumstances under which the sessions are cancelled (e.g. If the session is cancelled because the local authority/government states that the premises should be closed). If sessions are cancelled through fear of the virus, or because of a lack of attendance, but there is no local authority/government requirement that the premises/club/coaching session is closed/cancelled, most insurance policies will not respond. If you have a query regarding your business policy you should refer to your insurer or broker.