A lawyer practising in Guernsey is not simply practising English law. Guernsey law differs from English law (or even Jersey law) in many ways due to the Island’s Norman history.
The Channel Islands have been a part of the Duchy of Normandy from early in the 10th century. When Duke William II of Normandy conquered England in 1066 and became, additionally, King William I of England, the fate of the Channel Islands became allied to the English Crown. After King John lost mainland Normandy to King Philippe-Auguste in 1204 the people of the Channel Islands chose to remain loyal to the English Crown. The Islands were never incorporated into the Kingdom of England, let alone the United Kingdom. Through the grant of various rights and privileges over the years and centuries, the Channel Islands find themselves today as two separate and near-independent jurisdictions (the Bailiwick of Jersey and the Bailiwick of Guernsey), each with their own laws and customs; the Bailiwick of Guernsey not only includes the island of Guernsey but also the semi-independent islands of Alderney and Sark which are, themselves, separate jurisdictions within the Bailiwick.
However, the Norman origins of the Islands are fundamental to the practise of law in Guernsey. What distinguished Norman law was its customary law. Customary law has two senses in Guernsey law. It has a general sense equivalent to the English notion of common law, by which is essentially meant the evolving body of case law and practise as opposed to statutory or regulatory law. It is perfectly proper to talk of Guernsey customary law as a living thing being developed in the courts of the Bailiwick each working day. The other sense refers to the ancient body of Norman customary law itself which was developed from the 10th century onwards, and reduced to writing in the 13th, 14th and 16th centuries. The written customary laws, and the Norman, French and Guernsey jurists who commented on them from the 16th to the 19th centuries, remain a primary source of law in Guernsey to this day. The ancient customs of Normandy are still prevalent today in a number of areas of practise including, in particular, property law, inheritance law and enforcement of civil judgments.
The other principal source of law in Guernsey is legislation. Guernsey has its own legislative body, the States of Deliberation, which has the power to pass laws, with the approval of the Crown, in any areas with the exception of immigration and defence where the UK still has the power to legislate for Guernsey. It goes without saying that statute plays a significant part in Guernsey law with many areas of law now governed by primary and secondary legislation, especially in the financial services sector but also in relation to criminal law, employment law, family law and company law. In addition, and whilst Guernsey is not a member of the European Union, it does form part of the EU for the purposes of the legislation on free movement of goods and so EU legislation in this area is also applicable in Guernsey in the same way as it is in EU member states.
Despite the origins of Guernsey law in Norman customary law, and despite the wealth of primary and secondary legislation in Guernsey, the powerful influence which the English and Commonwealth common law has on Guernsey law should not be overlooked. It has to be conceded that in many areas of Guernsey law where statute or the customary law has not intervened, the influence of the common law (and English law in particular) is almost total. English and Commonwealth authorities are persuasive in Guernsey and decisions of the UK Supreme Court are treated with the highest regard. The common law in Guernsey is prevalent in tort law, many aspects of civil procedure and trusts law. Interestingly, the leading Guernsey case of Morton v Paint has also given the Guernsey courts some leeway to "legislate justicially" by allowing the common law to walk alongside statutory intervention in other jurisdictions where it is just and fair, and in the public interest, to do so.