Might be worth investigating that before doing much more. If there is reliance on an old storm drain or soakaway which has now ceased to function, that might be a big part of your issue.
Given the house has only recently been purchased (and therefore I'd guess insured), it is unlikely the insurers will get involved as this will be determined to be a pre-existing issue).I would check your insurance and then get them involved, as it could be costly and they will do all the liaising with neighbours and relevant parties and anything legal that needs dealing with or putting in place.
Is it pre-existing?Given the house has only recently been purchased (and therefore I'd guess insured), it is unlikely the insurers will get involved as this will be determined to be a pre-existing issue).