(1.23d).ToString("£0.00");

(1.23d).ToString("C");

var nf = CultureInfo.CurrentCulture.NumberFormat;
Console.WriteLine("CurrencyPositivePattern: " + nf.CurrencyPositivePattern);
Console.WriteLine("CurrencyNegativePattern: " + nf.CurrencyNegativePattern);
Console.WriteLine("NegativeSign: " + nf.NegativeSign);
Console.WriteLine("CurrencySymbol: " + nf.CurrencySymbol);
Console.WriteLine("CurrencyDecimalDigits: " + nf.CurrencyDecimalDigits);
Console.WriteLine("CurrencyDecimalSeparator: " + nf.CurrencyDecimalSeparator);
Console.WriteLine("CurrencyGroupSeparator: " + nf.CurrencyGroupSeparator);
Console.WriteLine("CurrencyGroupSizes: " + string.Join(",", nf.CurrencyGroupSizes.Select(gs => gs.ToString())));

Console.WriteLine((1232323d).ToString("C"));
Console.WriteLine((1232323d).ToString("£0.00"));

Thread.CurrentThread.CurrentCulture = new CultureInfo("en-GB");
var nfi = Thread.CurrentThread.CurrentCulture.NumberFormat;
Console.WriteLine(nfi.CurrencyDecimalDigits);
Console.WriteLine(nfi.CurrencyDecimalSeparator);
Console.WriteLine(nfi.CurrencyNegativePattern);
Console.WriteLine(nfi.CurrencyPositivePattern);
Console.WriteLine(nfi.CurrencySymbol);