Why use a recommended builder – aren’t they likely to be more expensive?

My general response to this would generally be ‘often – initially’. But in building terms the truism ‘pay cheap, pay twice’ very much holds good.
We currently have two projects running which require serious care and attention in order get the steelwork right. One contractor (McCabe Construction) used the detailing service of Bob Rich at B&M fabricators. The process was easy as Bob is a genius at fabrication drawings – any areas where there had been misunderstanding from the drawings were, within a few hours, ironed out between the engineers THB Consulting, the builder McCabe Construction, PPA Architecture and the fabricator B&M. The drawings were quickly amended allowing the contractor to proceed, and everyone was able to get the result they wanted.
The other contractor tried to get everything done cheaply and due to this was unable to get sign-off from the engineers for the fabrication, creating delays to the project. Time is money on building projects, as with everything else.
We had a project in Headington, Oxford a few years ago where the client was quoted £50,000 for a loft and extension by a contractor. We explained that she should beware as this was half the price she should be paying for this work, however the client proceeded.
The contractor was clearly inexperienced and the calls started coming to the engineers and PPA saying ‘why are the beams drooping, why to the first floor windows not shut anymore etc etc. The cost of remedial work to undo the damage would have been significant.
The building process can be easiest and as stress-free as possible if you use the right contractor. Your house is usually the most important asset you own, treat it with care and it will treat you well.