Forget it and walk away.

In your life you'll be offered or discuss, say, 50 - 150 jobs.

In perhaps one-third of cases, it will be a lowball offer.

In those 1/3 of case, forget it and walk away.

Regarding your language question,

I'm not sure how to best respond to the email saying that I really like the role and company, but I won't move for less than £35k without coming off as rude or harsh.

During your career, if you can't, simply, state your side in everyday salary negotiations, you're doomed.

Here's the language you need,

Dear Steve, thank you so much. As you know I am thrilled about every aspect of your company. I am seeking a 35k-40k salary at this time.

Rude, harsh etc does not enter in to it. Like everything else in life just state it plainly and simply and politely. Imagine you are asking where the toilet is - use the same tone and language.

If you actually want the 35, forget it and walk away.

In your life you'll be offered or discuss, say, 50 - 150 jobs.

In perhaps one-third of cases, it will be a lowball offer.

In those 1/3 of case, forget it and walk away.

Regarding your language question,

I'm not sure how to best respond to the email saying that I really like the role and company, but I won't move for less than £35k without coming off as rude or harsh.

During your career, if you can't, simply, state your side in everyday salary negotiations, you're doomed!

Here's the language you need,

Dear Steve, thank you so much. As you know I am thrilled about every aspect of your company. I am seeking a 35k-40k salary at this time.

Rude, harsh etc does not enter in to it. Like everything else in life just state it plainly and simply and politely. 

Imagine you are asking where the toilet is - use the same tone and language. Best of luck.