The vast majority of home insurance is transacted on line these days (either via a Broker, comparison site or direct) and most are not advised sales which leaves the customer to make his own choices as to suitability. The main reason for this is to keep costs down but of course this also means there is no money spare to pay people who know what they are about.
Generally you may find the tools and machinery "contents" are not excluded BUT some policies restrict the amount of cover in detached outbuildings or garages and in deed in some cases attached garages. it may be possible to increase the limits and may require improved security. However garden buildings are notoriously difficult to secure adequately and thieves are generally every bit as good at their job as anyone else is at their chosen profession, they also benefit from not declaring their earnings.
Regrettably the traditional high street broker is a rare commodity these days as they have gradually been forced out of business, sold up or the proprietors retired, previously they would be able to solve this problem quite easily. If you can find one give them a ring, they may be willing to help but don't be surprised should they refuse as premiums and hence commission is inadequate to cover the cost of experienced staff spending an hour on the phone taking information and then obtaining quotations. The project (work in progress) may not be covered as increasingly insurers are excluding "powered models".
Care should be taken when arranging separate polices to cover workshop tools and machinery as there is a very real possibility cover exists for these items under an existing home insurance. In that case there is dual insurance which although not illegal involves both insurers contributing to the loss in relation to their respective sums insured or limits. The technical term for this is "Contribution""and this concept will be beyond most claims staff and "Adjusters" at this level and a frustrating experience in obtaining settlement is on the cards.
If you are lucky enough to arrange cover please bear in mind that cover is on a "New for Old" basis and the sums insured should be calculated accordingly.