You should investigate your competitors’ designs and images carefully to check whether they are protected by UK or International Trademarks, Design Rights, Patents and Creative Commons Licences. The creators’ own websites should assert what special IPRs protect their works and you can also search the following websites:
UK Intellectual Property Office: https://www.gov.uk/government/organisations/intellectual-property-office
World Intellectual Property Organisation: https://www.wipo.int/portal/en/index.html
EU Creative Commons: https://creativecommons.org/
I am concerned that you risk an action for IPR Infringement, or if the designs and artwork are not protected, your competitor may sue you under the Tort of “Passing Off” as the two websites and products are sufficiently similar to create confusion in the minds of the public to the extent that you are exploiting the other business’s goodwill in a way that could injure it.
Damages for IPR Infringement are account of profits to the claimant for monies obtained through use of the work.
There is a six-year limitation period for a Claimant to issue Court Proceedings for IPR Infringement from the date that the infringement was first discovered by the Claimant or first ought to have been discovered. IPR Infringement is a “continuing tort” and a claimant’s cause of action in law against the defendant is refreshed each day that the tort continues. Therefore, a claimant may issue court proceedings, but damages can only be recovered for that part of the loss which arose within the six-year period prior to the commencement of proceedings.
You should seek legal advice as soon as possible after you are aware that you have breach other party's legal rights. I suggest that you instruct specialist IPR Solicitors to review this matter in full, advise you on your prospects of success and defend any IPR Court Proceedings on your behalf.