Landlord Tenant Dispute-Stolen art work?

It sounds like your artwork has very little commercial value and is special only to you as the artist. The landlord thought it was a piece of scrap metal he could use to mend the fence. I doubt a solicitor will be interested in pursuing this case for you in court because it is doubtful he could win and if he did the judgement would be minimal. Ask the landlord to provide you with the raw material and make a new piece and be happy. The part about second copies does not fly as famous artist make numerous attempts to perfect their art. Next time treat it as though it is valuable to you and do not leave pieces laying around in the garden. Good luck