The £1050 was paid through payroll. I was working in Portsmouth for 3 years when I actually have a house and live in Chepstow so the company said to sign up to their TAP (temporary assignment plan) instead of staying in hotels during the week which costs them to much. So I spent the extra money on a flat in Southsea £495 a month and living expenses so TV, Council Tax, Internet, TV lIcense, Electric etc. ( There was always a little more than needed but not much).
I live in Chepstow and my companies base office is Bristol. I was assigned a project in Portsmouth at a clients site for what was originally going to be a year. This got extended and extended as time went on.
Employment benefits are included in the calculation of adjusted net income for the purposes of the child benefit tax charge. You can deduct pension contributions. Take a look here for the calculation criteria.
If an employee is sent to work in a temporary workplace for up to two years, then it is possible for the employee to claim tax relief for the expenses incurred in travelling to that workplace or for accommodation costs. This type of claim is straightforward where the expense is incurred by the employer who obtains a dispensation from HMRC. As soon as it is know that the relocation will last longer than two years, then tax relief is no longer available.
As you will read here, it might have been possible to claim tax relief for the accommodation cost you incurred which would have the effect of reducing your income for the purposes of the child benefit tax charge. See the examples in EIM31838 here.
I suggest you make a claim for overpayment relief which you can read about here by writing to the tax office. I'm not saying that such a claim will work but it's a case of nothing ventured, nothing gained. You didn't say whether you completed tax returns for the last three years but that's where you should have claimed tax relief.
I hope this helps but let me know if you have any further questions.