Also to remember any company running a dbs check everything will show up spent or unspent convictions, even conditional discharges and cautions will show up. When your time has become spent you do not need to disclose obviously.... but when that dbs check comes up everything pops right up.
So nothing really gets spent or deleted with a dbs standard or enhanced check, and sadly UK employees will continue to break the law and decline anyone with a criminal record due to fear and not "risking" it for the company in case its part of Great Britain's attitude to cover their backsides first.... course you can disclose and depending on your offence and crime and job your applying for you may just get passed it all. Otherwise its live the lie which is the only thing you can do to support yourself and put bread on the table.
Moving abroad where less illegal checks occur or going self employed or working for family/friends or sticking to low level jobs ie in tescos where such checks don't take place much are the only options.
Having said tescos they too ask for criminal convictions on the app form, not sure if they would check it though fully...
As for taking a job and then bailing on the company.... just do it I once did not bother to turn up the next day and sent a letter saying I found another job. Not like I am going to see or speak to them again and if they are asking for a dbs check which imo is an illegal act itself due to privacy invasion and more so if its for a job position that is not deemed suitable for a dbs check then why bother with that company!
Goodluck with the job and hopefully its a job role that does not require a dbs check or basic check...