I've had quite a bit of experience with student loans, so I think I might be able to clarify a few things for you. I don't know much about your exact situation, so bear with me if you know all of this already.
1) If the problem is that your US loans aren't recognizing your UK studies and are therefore expecting repayment to begin because they think you aren't in school, then the fix is pretty straightforward. If your university is accredited in the US, just have them send a letter of enrollment with dates showing that you've never gone more than six months without half-time enrollment.
2) If you *have* gone more than six months without being enrolled half time, you may actually have to begin paying them back. You can get a financial deferment or forbearance for a period of time, but once that ends you'll simply have to negotiate a monthly payment plan and there's no other way around it.
3) If you've only dropped below half-time enrollment for more than six months due to maternity leave, then your lenders may have provision for this. I assume that you've already contacted them, but if not explain this situation to them and provide any proof necessary to get them to extend their six-month limit given the maternity leave situation. If they don't have provisions for maternity leave, then unfortunately, again, you'll have to start paying them back.
*** I don't know if there are many professionals in the UK that specialize in mediating students and US lenders. I'm not particularly certain there are many companies in the US that handle this, either, but if there are then those are your best shot. Most of the companies that I know of are debt consolidation specialists, not advocates or intermediaries. If you simply want to negotiate more manageable payments while you're in school, then I'd recommend contacting one of these US consolidation companies who can whittle the payments down for you.