Can I get a loft hatch with ladders for a 410mm X 610mm clearance or do I need to extend.

you will be able to get a ladder in this space but will most likely need to custom build a hatch.

Hi, generally the opening required for combined hatch and wooden ladder system is 1110 mm x 560mm. on a modern house with roof trusses at 600 centres the opening will only need to be extended along the joists. This is fairly easy to do , and apart from light sockets or smoke alarms in ceiling will cause little disruption.I would recommend getting a carpenter unless you are a dood DIY person, anyway you will need an extra pair of hands as they are quite heavy. I have done them on my own, but would not recommend! If you have an older house say pre 1980s, then it is likely that you will have to trim opening (carpenter needed) and if you have old lath and plaster it can get VERY dirty. Use a product called roll and stroll to protect carpets, but do not use on hard floors! Lath and plaster is very unpredictable in terms of the plaster staying attached to th laths so when you cut larger opening unstable plaster can fall off. However whatever you do when finished the improvement will be well worth it. Good luck. Charlie Bates