Before subscribing to a rights issue, it's important to check the required funds for the subscription. You'll receive an email with the amount needed. The subscription price for each newly issued share is usually lower than the current market price.
If a company announces a rights issue with a subscription price of £45 and you don't have enough funds, you won't be able to subscribe. To participate, you'll need to increase your available funds by depositing money or closing a position. Once you have enough free funds, you can try subscribing to the rights issue again.