VS-LHRCSA please only post what you know to be entirely correct. Do you fly for BA??
Ok in answer to your question you are always paid your basic however BA also give you a training allowance. This is less when you are training at LGW but when they send you up to LHR the allowance goes up for the week and a half you are away. It totals approx £300.
So in effect month one and two do have allowances on your payslip but budget for basic + £150 for months one and two.