If that inverter can run each as separate strings you'll be fine.

Edit: looks like you're in luck:

http://www.solarmax.com/gb/en/products/string-inverters/solarmax-p-serie/?tab=specifications

Steamy - thanks for the suggestions, will keep this in mind.

If the installer goes bung off and I'm left with the Innotech EcoPlus 250wp panels and a SolarMax 4000p inverter, is it any good or should I be looking for better?

Have you considered having a few more panels on one or both strings?

OK, you drop down to the next FiT rate (I'm 99% sure) and there would be rare occasions that this would clip at the 16 A (3680 W) limit but most of the time you'll generate more power. Some arithmetic is needed, taking into account your position and any shading, to see if the extra capital investment and lower FIT rate makes it worthwhile. A small increment probably won't be worthwhile but a few more panels might well be.

It's particularly worth considering on split SE/SW (and especially E/W) systems like this because they're even less likely to run into the 16 A limit. When one set is full on to the sun the other set won't be.

Take a look at REC panel , very good market leading EROEI (CO2 payback etc.) robust construction.
Also I've fitted a lot of Aurora power ones PVI-3.6-OUTD , 2 strings , separate mppt or you can parallel strings.
Robust, simple , easily adjustable start voltage for each string (lower than SMA so kicks in at lower light thresholds)
Re. system size. I'm still of the mind its the DNC declared net capacity (inverter output) that's important for FITs banding, which by G83 is 16A 3.68kW . Total W installed of generators ( PV panels) is a different thing .
Though I'm not sure most FITs supplier might agree, especially as for the last few year they've been asking for this on their forms as well as DNC

Thanks Ted , do you know where previous installs that took DNC to equal TIC will stand ie. installs with TIC slightly above 4kWp but registered DNC 3.68kW now this has been clarified, especially those dating back several years ?

if under 4kWp (DNC=3.68kW, 16A) the installation company will inform DNO post installation via G83, no additional cost.
>4kWp then G53 need to be organised prior to installation with possible DNO inspection and cost to upgrade local transformer.

We initially installed a <4kwp system, then last year decided to double the size of the array. When we initially enquired, we were told that a G53 relay needed to be installed by the DNO, which was going to cost just under £4K. The installer suggested changing the inverter to a G53 inverter, which the DNO accepted (no requirement to upgrade transformer). We did however have to pay a fee to the DNO for permission, £595 if memory serves.
We now have two arrays one E facing < 4kwp and one S facing <4kwp, each array on its own inverter string.

FiT wise, we retain the original, 4kwp system FiT of 21p, and receive the system > 4kwp tariff of 13.99p for the additional panels we installed. Our final FiT rate is calculated on the % output of each array - e.g. 51% of generation at original FiT and 49% at new FiT, in our case around the 18p mark. Be aware that the final % used are based on declared output rather than actual. In fitting east facing panels we do lose as declared output based on maximum south facing output.

We have just the original meter. My original system retains the original FiT rate, the new system is on the >4kwp tariff of 13.99p. The systems are still treated as separate for the purposes of FiT based on declared capacity and installation date.

Yes, both array's have to be on the G53 inverter. It was the DNO that specified that a G53 relay had to be installed, and replacing the inverter was the simplest and cheapest way to do it - added around £400 to the cost of the 2nd system if memory serves. Had we paid the DNO to fit a G53 relay on the network itself, then we could have gone down the route of 2 G83 inverters, 2 meters etc.

Had the DNO insisted that the only way was their way, we would not have installed the additional array. I assume that larger arrays, such as those on commercial buildings/ farm sheds etc already use the larger inverters so suspect it wasn't really something they could force on us given that the inverter could be specified with the required G53 relay. My experience however suggests that there are not many residential installations that have been extended in the way I have, as advice and information was a bit patchy - FiT provider giving conflicting info, DNO initially being inflexible.