Many houses around here have 3 phase electrical supplies whilst in Britain this was usually only supplied for industrial uses.  The reason is largely linked to the size of the country and the distance between settlements.  Electricity is generated in three phases and supplied down to local transformers in that form.  The use of all three of these phases in a property means that the load is spread over three cables and therefore these can have a smaller cross-sectional area as they carry less current and are therefore less expensive.  The downside of a three-phase supply is that if too many domestic appliances are used on the same phase at the same time the supply may trip off because the current has exceeded the tariff at the meter.  If this were a persistent problem, the solution would be to ask a qualified electrician to check that that the system was balanced out correctly.  However, on an old installation, which had evolved in an unbalanced way over the years, it might be necessary to consider having your supply changed to single phase.  This should be straightforward but again, consult a qualified electrician, who can advise you accordingly and make the arrangements with EDF.