Need new soakaway but can't fit one 5m away from house

Hama4075

I have a house built in 1960 and have just had the back roof rainwater drainage checked and CCTV'd.  The soakaway is finished and needs to be replaced (it's beyond jetwashing).  The issue is:

- my back garden is small so there isn't a 5m distance from the house (more like 2.5m or 3m) 
- the house and my neighbours' houses don't have foulwater drainage at the back that could be connected to (if permission was given) - all that's at the front 
- I want whatever I do to meet building regs/have Building Control approval

The drainage company I'm using (who have a good reputation and are recommended by structural engineers) think that a replacement soakaway can be installed in the back garden closer than 5m since there aren't any other options.  They don't seem to be planning to check with Building Control, although they want to put the new soakaway in a slightly different place from the old one so I think it would be classed as new.  Even if it went in exactly the same place as the old one, they recommend a slightly bigger one.

I want to make sure that what I do isn't going to cause any problems, and also that it has the right paperwork for whenever I come to sell the house.  Can anyone advise?

In particular I'm wondering:

• Should I pay a properly qualified engineer who specialises in drainage to advise on the situation?  eg a civil engineer or structural engineer?  If so, how would I find someone with suitable qualifications and drainage knowledge?
• Should I ask Building Control to visit and give advice on what to do, or is it better to draw up my own plan first and just ask them to approve it if special approval is needed?

Are there other alternatives to a soakaway in the garden?  The only two I've come up with are:

• Ask the water board for permission to connect to the foul water drainage system.  Unfortunately, in my case that's quite far from the back of the house so it would involve extensive pipework, including under my driveway, and be very expensive
• Build a soakaway under my driveway, which is behind the back garden so could be 5m away.  Again, this looks like a very expensive option with lots of excavation and pipework, and reinforcement over the soakway

Would be grateful for any advice or ideas.
Thanks.

Ectophile

I would go for the "it complied when it was built" argument, and just repair the old soakaway.  I assume that means digging out the years of accumulated muck, and then re-filling it with gravel.