This little anecdote is actually typical of the pointless difficulties created for SOs. This is why openness and honesty don't always pay.

Hi
My Offence
I am an ex offender, my offence was basically that I paid for sex with a female who turned out to be under 18yrs of age. A fact I did not know. I only pleaded guilty because "I said yes".
I will not go further into the details except pre-sentence I was told 30 mths supervisory but got 4 yrs, so on the SOR for life or until I apply in a few years. 
I have had numerous psychological assessments that agree I have NO paedophile tendancies etc, found unsuitable for any type of sex offence course and always classed as low risk.
The Judge and CPS both stated there was no grooming or predatory actions and they knew she was "working the streets".
Searching for work
I will start by saying I have worked in the recruitment world for some years so understand their mindset.
When required, I have always declared my offence, regret and understand my lack of morals towards the female either to the recruiter or the employer. This has know made me secretly "blacklisted" by recruiters.
I have applied for over 2000 jobs and still unemployed, with the majority of rejects due to my being labeled as a "sex offender". Though now the time elapsed since my last role is also being a negative.
When I have not be required to disclose to the recruiter - because they haven't asked the correct question - I have managed to gain face to face interviews and actually been successful in receiving offers. I look back at these offers with a sense of pride - in that someone has recognised some worth in me - and amusement but sadness in their confusion, lack of acceptance or understanding in the different types of "sex offence" as they would do if my offence was one of violence or drugs. However it is mainly their lack of compassion towards or belief in rehabilitation especially when they have just spent time explaining how supportive the business is to its employers. 
 
Your example talks about "volunteering" and "charity" shops which is a topic I have discussed with my PPU. I explained to them that the ones I have considered applying to all require a declaration of the details of the offence to be documented in detail. Having created a new identity, moved and now living in a reasonably small place were gossip is common, how do I know my past will not be revealed due to no security processes being in place or regulated.  It is easy to talk about "data protection" but we have to be realistic about how a lot of these types of businesses are run. No offence meant.
To finish, my experience has also shown that even the PPU can be a major obstacle and will show discrimination under the heading of public safety.
For example, when I told my PPU I was going to apply for a weekend role where I would escort prospective house buyers around empty houses on behalf of a Estate Agents - who had not asked for a declaration. My PPU said they would tell the Estate Agents. Their reason being, I could go to a house where a "child" might be by themselves. Hence my lengthy beginning to this reply and my formatting the word "empty"  as I did.

I wish you luck in gaining the examples of others and look forward to reading your report. If I can be of assistance I would be happy to "find the time" to do so. lol

Learn from yesterday, live for today, hope is for tomorrow else what is left if you remove a mans hope.

As an ex-offender I have had the opportunity to help the community by paying back through volunteering for charity, retail outlets. These as we know are non-profit making organisations, however they seem to have a varied approach to the recruitment policy and risk assessment of ex-offenders (if they even bother!). What I think needs discussing is that for certain individuals volunteering in this field is, for some, the best way to re-integrate and overcome the usual post-release depression and anxiety. I would like to collate people's experiences and write a piece for theRecord. For an example I have an ex-offender acquaintance who had been volunteering for a charity retail outlet; risen to the dizzy heights of key holder/relief manager; completed 18 months of said same blemish free and then was black balled as the charity suddenly altered their recruitment & retention policy making the unblemished record worthless even with the support of their ex-offender manager (who wrote to the CEO!)and their explanation of the word 'rehabilitation'. It destroyed my acquaintance and their belief of the existence of an understanding society.