If in doubt, always seek the advise of a qualified electrician, however, as a general rule, a standard 13A plug socket can take up to 3kW of heaters. That can be 4 x 750W Tansun Carnival, 2 x Helios Top 1.5kW or anything else as long as the total wattage is below 3kW. Once you go above 3kW it is necessary for a qualified electrician to wire a suitably rated spur and for him to connect the heaters up to it along with any switches required.