contract of sale is with retailer and customer, nothing to do with the supplier to Evans. If the bike has quickly broken, its up to Evans to sort it out with their supplier. Telling customers "its going back to supplier or manufacturer for assessment is typical B.S. the bike industry likes to tell to clueless customers
Probably 90% of the items that have been returned to wherever I've worked have been returned to manufacture/distributor for inspection before a decision has been made to offer refund/replacement/tell them to jog on.
I would quote "goods not fit for purpose" and ask for a new bike, or a full refund, well within your rights under consumer law
Evans are also well within their rights to inspect the product, How does the shop assistant know its not neglect/crash damage.
It doesn't sound like the process was explained well by Evans, or your the OP's mate got the wrong end of the stick.