With every type of business insurance, you should always ensure that all of your business activities are adequately covered by your policy. This may seem fairly obvious, but certain insurers can use the small print in the policy wording to deny liability for a claim because they were not aware that you were doing a certain type of work.
Insurers do of course allow there to be a certain amount of leeway, for example they accept that in a public house there will possible be live music, the odd band or maybe other entertainment. What they will need to know is if you have, for example, a disco every Friday night, where people pay to get in and you are open til 3 am on Saturday.
As far as restaurant insurance is concerned, they accept that you may have private functions and possible undertake him deliveries. But, if you undertake outside catering, this is something that insurers should be advised of, and your policy documents should note this.
Outside catering presents increased risks for the business, on both the liabilities and the damage to property front. Depending on the amount of time that you undertake for this activity they may wish to apply certain terms and conditions or alternatively charge a higher premium.
If you hire in waiting and serving staff, this increases the employers liability insurance risk. You have staff that you may not be used to working with, may not be fully trained and they are working in a strange and possible busy environment. As far as the property risks are concerned, you have the increased chance of damage being caused for your equipment, maybe portable heating equipment and furniture.
Most insurers are reasonable about this and will simply endorse the policy to note this without charge or amending the policy. Others however (usually the ones that quote the cheapest premiums at the outset) will try an recoup some of their money by charging you for the changes to the policy. If the charges seem unreasonable, then challenge them and see whether they can be removed or reduced.