Financial assistance for raising EPC rate?

The report from the assessor will indicate improvements, what effect they might have and also give indicative costs for carrying out the works.
I would wait for the report, decide what you want to do and then source funding.

If its an A rated condensing combi boiler, plus the radiators have thermostatic valves, there is a central heating timer/thermostat control (idealy in the living room), plus loft insulation (best is 270mm) and you make sure all bulbs are energy saving, on experience from my victorian properties you should pass easily.
Apart from double glazing If you wanted to do more internal wall insulation is cheaper than external but you do loose about 100mm off the room dimensions.
Note that EPC assessors can only count what they can see or that you can prove so make sure they can access the loft and take photos of any insulation works you do and keep a paper trail.

If you (having turned off the electricity) undo a plug socket and pull it forward, the internal insulation should be evident to the EPC inspector. But better to take lots of pictures as its fitted

An alternative to replacing existing sash windows is to install secondary glazing panels which can be fitted inside existing window recesses. These will be significantly cheaper than replacing the windows.

You should check with your local authority that you are permitted to replace the windows and whether it is listed or in a conservation area in which case it might be exempt

Double-glazing is largely a waste of money in terms of the energy saved, let alone the cost - you certainly get very little credit for it in the EPC ratings - just 2 stars out of 5. I think the payback period for owner-occupiers is something like 25-30 years, even assuming they are fitted properly without cold bridges between the new windows and the brickwork, which leaves plenty of time for the PVC to yellow, the glazing panel seals to fail, and your d/g company to go bust, invalidating the guarantee. You will probably get better value for money by using secondary glazing and investing in a thorough programme of draughtproofing.

You will also get EPC credit for insulating under the ground floor, so again this may be more cost-effective than double-glazing to reach your E target.

Internal insulation usually ruins any original features in the property, and there's all the hassle of moving everything that's mounted on the external walls (baths, radiators, electricity points and meters, etc etc). You will also want to check very closely that your builders know what they are doing around the window reveals: plasterboard butted up against the original plastered brickwork can look awful, especially if the guys who do the work prove incapable of using simple tools like a square and level.

External insulation is less invasive on your interiors, but has problems that are equally unpalatable and expensive: there's all the soil pipes and guttering to move, the loss of original feature brickwork, how to create effective reveals around the doors and windows, working out whether the original roof overhang remains sufficient - the list just goes on and on.

It should be possible to reach Grade E without any internal or external insulation, but if the Government ever goes crazy - and I fully expect that homegrown British bureaucrats post-Brexit will be just as capable as EU ones at inventing "energy saving" regulations - and requires all rented houses to reach EPC Level D or higher, it will be extremely difficult for landlords to reach this without major intervention in the fabric of their buildings.

You may be interested to know that Historic England takes quite a dim view of double glazing in terms of the overall upgrading of a property with sash windows.

This link may prove useful:

https://historicengland.org.uk/advice/your-home/saving-energy/older-houses/sash-windows/

There are better Historic England pages on this subject somewhere that I have read in the past but in the limited time I currently have available I do not have time to ferret them out.

The content behind the supplied link should give you a good enough steer to dig it out though and when you do it might be worth waving it under the nose of your assessor.

Really important - no-one has mentioned to you that the govt has already announced that the thermal quality of solid wall properties has hitherto been underestimated. They will (at some point) be reviewing this and it will have an impact on EPC assessments. We are therefore waiting for our EPC assessor to let us know when new guidance is issued before getting a new assessment. If your EPC person has not mentioned this to you already - they should have done - as it is they might do your assessment now and you could then have to have another post new guidance - waste of time and money. There is a page on the RLA website under minimum energy efficiency standards that talks about all this.

Over and above this then having fitted a gas fired condensing boiler in laymans terms almost guarantees your property being E or above - I doubt you will have any more to spend.

We used a company called London epc (www.london-epc.co.uk) to carry out energy surveys on a block of flats we manage. They basically came in to ensure we met the MEES that are due to come out in 2018. I was actually surprised as although all the properties are solid wall construction and they have very very old double glazing, they all actually met the required efficiency without having to carry out any works. Basically they come out and do initial surveys and they then tell you what needs to be done to get up to ensure you comply. They say boilers, cavity wall insulation (where possible) and loft + energy saving lighting are the things you need to hit first in terms to bump your rating. Seemingly though it shouldn't take much for all homes to reach this levels.