Citybird;
Firstly, becoming a LP was not a lifestyle choice! XH left us, and contributes £0, not even a christmas or birthday card in 5 years.
Being unable to get a job which pays more than the one I do currently is not a lifestyle choice, either. In fact, I consider myself very fortunate in finding a job which pays more than the NMW (7.05 p/h). I work 30 h/w, as that is the maximum hours I can do as a TA. If I got a job working 9-5, 37 and a half hours (official full-time) I would have to get a minimum wage job (as this is a rural area with few job prospects), a dead-end job, therefore earn no more money, but be significantly worse off emotionally and worse off financially due to extra childcare costs.
If I got a weekend/evening job, I would firstly be very tired and unable to care for DS, secondly, who would look after DS? More childcare costs ?(if possible at all, there are no ofsted registered weekend/evening childminders here). Plus, I would be unable to continue studying part-time for my degree, effectively trapping us into a life of poverty.
You are right, if I work more, I will be penalised by having to pay more tax, and have my TC reduced, so I will not actually be any better off. It is a disincentive. But, if you take the TC away, and I have to work more hours, as I have already explained, my childcare costs will go up, and my earnings will not cover the loss of income from losing TC.