You actually have a statutory duty to have insurance when you own one of the flats in a tenement. It's possible that the title condition goes beyond this requirement in some way, but there is still a minimum level of coverage. This is in the Tenements (Scotland) Act 2004, s.18. It says (together with a statutory instrument outlining specific risks, such as fire) that you need insurance coverage for the reinstatement value of your property and any associated parts of the building (the "pertinent"). The title deed may specify the allocation of common parts to different owners, and there are fallback rules in section 3 of the Act to make sure that everything is the responsibility of somebody.
The owners of other flats can ask you for proof of insurance, and you have 14 days to comply. If you do not, then they could take you to court, and the court could order you to get the insurance. As described in the Act, compliance is not required if the cost of insurance would be "unreasonably high", or if it's unobtainable after "reasonable efforts". But in a situation where other owners have been able to obtain insurance, and you could afford it in principle, the reasonableness standard could be hard to refute. Violating the court order means that the consequences escalate. Legal expenses can quickly outpace the cost of just getting the insurance.
Sometimes, flat owners club together to obtain a single insurance policy for the building. (Naturally, everybody then has to bear their share of the cost.) This can be fiddly to arrange because of the coordination involved, and the interaction with other people's existing insurance - such as policies they have because of a mortgage, or to cover the contents of their properties rather than just the structure. The way this works also depends on the mechanisms in place for common decision-making; there's a scheme in the Tenements Act which can be followed if the deeds don't already specify.
As mentioned, the deed of conditions might go beyond this regime in some way, for example by giving the council the power to request proof of insurance. Enforcement of a title condition works in the same way as the statutory condition. In the case of building insurance, any of the other owners could bring a court action, because they have an interest in the fabric of the building being maintained. Generally, title conditions can be varied either by agreement, or as a result of an adversarial court process (in the Lands Tribunal). Either way of proceeding would end up involving the other flat owners as well as the council, and would entail instructing a solicitor.
I assume a solicitor is already involved in your proposed purchase. They would be able to give more specific advice if there is something objectionable in the deed; the condition in the Tenements Act is not negotiable.
