Pedantic point - there is no such thing as an "artificial flavour" in the EU any more. I'm still shocked at how many labels have "no artificial flavours" on, but clearly the regulators are somewhat indifferent, as I can't see how this is anything other than a very clear contravention of Article 7(1)(a) of Regulation (EU) 1169/2011 - there is literally no food on sale in Europe that contains an "artificial flavouring", as the definition no longer exists as a legal name since Regulation (EC) 1334/2008 came into force years ago. Sorry, rant over, back to your predicament
I don't see a significant issue with the "no added preservative" claim, as citric acid is used as many things other than a preservative (it's not like e.g. Potassium Sorbate, where the primary use is as a preservative) and you probably won't be declaring it as a preservative - the specific function it is performing in your product is increasing the acidity, so I'd guess you'll be declaring as something like "Acid: Citric Acid" (see Annex I of Regulation (EC) 1333/2008 for the various "functional classes" for additive declaration). This would be broadly the same for any other acid you'd used (e.g. the lactic suggested above).
Do be aware that it will still have some impact on taste, although you won't get the increasing lemon flavour that comes with adding more lemon juice.
If you're still wary of the citric acid option and/or want to persevere with lemon as the more "natural" approach then could be worth trying some different lemon juices, as I know this works successfully for the majority of the hummus produced in the UK. By "fresh" lemon juice, do you mean directly pressed from lemons in the UK?
Personally I'd be inclined to try:
Lemon Juice NFC - similar characteristics to "fresh" lemon juice, but widely available in aseptic drums / bag in box, so a nice low incoming micro count and long shelf life.
Lemon Juice Concentrate 30-32 Brix - fairly standard option so widely available, works out cheaper per kg of lemon juice, and I know that it can work well for hummus.
Lemon Juice Concentrate 400GPL or 500GPL - highest acidity levels you're likely to routinely find available (it is possible to go higher, but not common to do so as it can be quite detrimental to the flavour profile), and whilst I don't think it'd be necessary to use either of these, it may be an option to try if nothing else is working for you.