I think you can only avoid a house when you go into care if you were living there and you had no where else to go. A lot easier if there is a spouse.
It will be worth talking to a solicitor to put the house in trust to avoid this. Wish we had done that for my mum's place. However, if there are signs that your mum's health is getting worse you may not be able to avoid the house being used to fund care. Acting as early as possible is the best advice you can have. Care has cost my mum in excess of £150K so far!
The other alternative might be for you to buy the house outright for your Mum. Thus allowing your Mum to have some extra income to enjoy or distribute to you and your brother. If you have a property and an older relative lives in it and you pay for everything I believe you can avoid paying capital gains tax. Your Mum will not need to pay for care if she has spent all the cash before she gets to that stage.

Why not remortgage your own house to raise the extra cash ? You look like you've got enough equity to still get one of the better rates. Much cheaper than an unsecured loan.

Then you give the cash to your Mum but register a charge against the property she will buy so you get your money back when it is sold (for whatever reason). That way there are no complications with your brother on inheritance as your £25k will come out of the house value before the remainder is split 50 / 50. No CGT either as you don't own the house (or even part of it).

If you have a joint mortgage with your Mum the mortgage provider will want you to be named in the deeds and you'll need to get an agreement drawn up to make it clear that the ownership isn't 50 / 50. There would also be CGT to pay when the house is sold on your share.

I'm not sure about the care point but suspect you can't avoid a house sale if she has to go into care.

Would your brother not be contributing?

My Mum really wants to move and I want to help her...she currently owns her own house outright, I have my own house (it's mortgaged about £230k, value is £300k). I have good job and excess cash each month.

Mum wants to buy a place worth £145k and she can raise with house sale + savings about £120k.

So I need to raise £25-30k. question is, what's the best way of doing this, do I:

1) Go into a joint mortgage with my Mum, so I effectively pay the mortgage but it's in both our names (we wondered whether this may make it less likely that Mum would need to sell her home if she ever went into care) or

2) Just take out a personal loan for approx £25k - I can raise between 7-10k in savings if I need to.

Any ideas??

Mum will be leaving half each to my brother and I and we were going to get an agreement set up for me to get effectively my share increased given my injection of capital.