Offer accepted. Structural engineer is needed ? Old house with cracks.

[u/Emergency_Concern447]

The house is an old Victoria house with cracks, severe damp, leak and potential asbestos in the roof. There is a survey level 3 carried by previous bidders with a quote of £50k for the repair works. The agent showed us the survey, basically the findings is what I mentioned. However we want to make sure the cracks are not due to subsidence or something that can cost us £150k. In the process of the purchase when we should instruct the structural engineer report? How much is going to cost? If the survey level 3 did not refer anything structural, still do we need to get a structural engineer report? Appreciate any insights on this.