I'll bite. (Day job: Theatre Consultant, although not in the UK.)
Why so?
I do competitive tenders all day every day. I issued 4 last week and have two more going out the door today...the spring is brutal... Yes, they do sometimes go wrong. But not that frequently.
An older Theatre Consultant I know (actually at a different company, not my employer) once told me: "They'll notice the one thing you get wrong, not the 10,000 things you get right." Consultants are human, fallible and do make mistakes, but I would contend that the situation without access to them (particularly in orgs that don't yet have any technical staffing) would be much, much worse.