Thanks. During construction you could have applied for an injunction either on the basis that the neighbour had failed to comply with the party Wall act and said you notice or on the basis that he was trespassing on your land and on the basis that the windows overhang land with open without lawful authority.

the difficulty at this stage is that the neighbour will argue that your failure to take action in the last couple of years amounts to implied consent and that you are estopped from taking action now. It is probably unlikely that a court would order that the extension is removed from your land at this stage. It may be prepared to consider the issue of the overhanging windows. You may be limited however to a claim for compensation at this point.

I would suggest if you decide you wish to pursue this at this stage, you will need the representation of a solicitor and surveyors report together with recommendations for you spend money on court fees issuing proceedings which may be limited impact at this stage. It may well be a you have a reasonable claim to compensation and may be able to seek to stop up the windows so that they cannot be opened at delay can be fatal in these sorts of situations in terms of actually having the structures removed