I applied online. The process took 1 week. I interviewed at Shell (Leeds, England) in Jan 2016
Interview
Submitted CV online and had an interview within a few days in the office at the petrol station. Standard questions asked about experience and your strengths/weaknesses. Nothing tricky involved. Whole process was completed within a week.
Light conversation asking if you're flexible. No real assessment. If you work in retail before then you will have a much better chance of being hired. I wouldn't say you need to worry too much about the interview.
