TNEI Services interview questions

Group interview which was delivered professionally. Questions were of reasonable difficulty, and included technical questions about power networks, about C++ and about tooling. I was offered the job in writing and was asked to state salary expectations - and asked for £45k which was significantly less than my pay in a previous job which had very similar responsibilities. The offer made by the TNEI was inflexibly below market at £35k. Note that Petrofac, the petro-construction company that owns TNEI pays its software engineers £50k+. So negotiations broke down and the job was given to someone else. But this was dealt with in a very unprofessional manner by HR - they increased the pay by £2k to £37k, then I (naively) accepted the job over the phone. When asking for confirmation in writing, I was told that the job was instead given to someone else! This is extremely unprofessional. It's become clear, and I have been later advised that I dodged a bullet - that this company is likely to be lowballing its engineers, who otherwise seemed very qualified, capable and driven.

Normal interview process for this type of job. Classic interview questions, why do you want to work here? Why this company? Why data science? Some basic questions about coding and other simple maths.